The Hi Power, P-35 or by whatever name it is known is definitely a classic of proven, tested design. Some do consider it "obsolete" and "outdated". I consider it a favorite and expect to for years to come.
The choice is there in action types, too! We can still find purely single-action autos from a number of makers including FN, CZ, and a number of 1911 makers who chamber it in 9mm. Traditional DA/SA automatics can be found from S&W, HK, SIG-Sauer, CZ, and more. Want a "plastic pistol"? You can sure find in from Glock, SA with their XD9, S&W, and others. Some such as CZ and HK offer selective single-action, meaning that their DA/SA pistols can be carried cocked-and-locked.
For me, the Hi Power continues to remain my favorite overall.
Part of this is admittedly subjective but some valid arguments for the "mature" Hi Power design can be made. So let's take a gander at why this classic design continues to be popular with folks interested in something to take to the range to those most assured that they will go in harm's way.
Simplicity & Reliability: The Hi Power consists of very few internal parts compared to many of today's handguns, but it is not alone. Others include the aging Makarov, the 1911, and the considerably younger Glock. All of these pistols share a common trait and one that is frequently espoused by their devotees: reliability. Each of these guns has proven itself capable of functioning under adverse conditions. The ultra-fine sand of Iraq may affect one more than another, but that pistol may do better in arctic climates. The Hi Power has been doing this decade after bloodletting decade. I am not saying that more internally complex handguns are doomed to be unreliable; I am saying that the potential is there.
With older classic Hi Powers pre-dating the Mk II which arrived in the '80's, the Hi Power's legendary reliability was primarily with FMJ or ball ammunition. It is very true that many of these guns simply would not run reliably with other than jacketed round nose ammunition. Their humped feed ramps worked great with military-style ammunition but could be very selective about which JHP ammo they would feed. With some work on the feed ramp this could be changed and I've done that very thing with a couple of my older Hi Powers. They handle any JHP I've put in them since. With the Mk II and it progeny, the Mk III, there is no such problem. FN finally went with a feed ramp capable of slickly feeding about any JHP.
Today it seems that the few reliability complaints with the Mk II or Mk III pistols are not feeding, but extraction. With enough ammunition fired, it is possible for crud to build up under the extractor to the point that the claw does not move inward enough to get a complete "bite" on the cartridge rim. A failure to extract can be the result. Simply removing the extractor and cleaning out the mess usually solves the problem and it is not chronic; it occurs after many rounds have been fired, assuming that parts are in spec…and they usually are.
The other "problem" with the Hi Power is that the extractor spring must be a strong one. Pushing inward at the rear of the extractor should require pretty good effort to move the extractor. If it doesn't, the spring needs to be replaced. (I've had really good luck with Wolff extra strength extractor springs.)
That's about it. Clean under the extractor every case or two of ammunition and you should be good to go and check the extractor spring. If you unexpectedly begin experiencing failures to extract and the extractor claw is in good shape; I'll bet the problems either crud under the extractor or a weak spring.
Reliability is desirable at the range. It is essential for self-defense whether fending off felonious assault as a private citizen, shooting it out with a criminal as a peace officer, or dishing out defeat to enemies in war.
The Hi Power will reliably pop any primer I've tried. This includes the very hard-primed Greek ammunition sold in droves here a few years ago. Glock 9mm's simply did not get 100% detonation. Neither did S&W 9mm pistols. The reason is that the Hi Power has a hell for stout mainspring. I am not aware of another handgun mainspring rated at 32-lbs. The striker on the Glock and the S&W with it's lighter mainspring simply couldn't overcome each and every single one of the hard Greek primers. A few months after its debut, ads for the Greek surplus stated, "Not For Use in Glock Pistols". At this point I should mention that this stuff was probably excessively hard primed, possibly for use in open bolt submachine guns. (Glocks and most other quality 9mm automatics have reliably fired most every other military round I've tried or seen shot. I know they've been reliable with any and all US-manufactured ammo I've tried.) Still, this speaks well of the Hi Power. The change to the heavier mainspring took place in the '70's with the "C-series" Hi Powers. I was told at the time that this was not necessarily to increase reliable primer detonation but to help the pistols withstand some hot-loaded SMG ammunition being used in the unending unpleasantness in the Middle East. The heavier mainspring works similar to a heavier recoil spring in delaying the slide's rearward movement and slows slide velocity to avoid rounding locking lugs on the barrel. Still, it is a good thing to know that the pistol is capable of reliably firing most any 9mm cartridge made in the world. (The only primers I've seen fail to fire in the Hi Power 9mm and .45 1911 have been in factory Sellier & Bellot ammunition. In these cases I believe that the primers were defective. Both pistols had full-strength mainsprings and the same rounds failed in other pistols as well. I have not seen this repeated in several years but still have a hard time trusting S&B for anything other than the range.)
Accuracy: This is a relative term. To a formal match pistol shooter, the Hi Power is an inaccurate handgun. To the less-than-stellar shot, that the gun will keep its shots on a piece of typing paper at 10 yards might mean that it is very accurate in his estimation. To me the Hi Power is a very accurate handgun considering that its original intent was not to wallow out a single hole at 25 meters. Having shot lots of Hi Powers over the decades, I submit that most will put 10 shots inside about 2 to 2 1/2" with ammunition that groups in that gun. I've seen it consistently group better than what some gun scribes euphemistically call "acceptable combat accuracy." A Hi Power capable of but 3" @ 25 yards would be dropping any shot no farther than 1 1/2" from the POA, assuming zero error on the shooter's part…which is rare.
For those wanting greater intrinsic accuracy in their Hi Power, a fitted BarSto barrel will usually reduce group size by 15 to 20% with most jacketed rounds and more with cast bullet loads, at least in my experience. The 1:10" twist of the factory barrel works with some cast loads, but the 1:16" does better in my experience and with a wider variety of cast/plated bullets. The majority of my Hi Powers use their standard factory barrel, as they're plenty accurate enough for my purposes. For a general-purpose sidearm, if I can hit a target the size of an orange at about 25 yards that's all I require. This does not mean that the Hi Power platform is incapable of better accuracy. The target version of the gun, the FN Competition, is capable of very small groups, but the gun is no longer produced; no demand. It appears that fans of the Hi Power find it accurate enough in standard trim for their intended needs.
Here we see two 15-yard, slow-fire groups fired with a Mk III Hi Power using the standard barrel w/o any "accurizing" other than a good trigger-pull. These were fired from a seated position with my wrists braced and bagged. No effort was made at speed. For me, this is plenty accurate enough since I cannot match these groups off-hand. Thus, I cannot shoot beyond the intrinsic accuracy level "built" into the gun. Others might but I cannot.
The thing that really contributes to the Hi Power's accuracy for me is its practical accuracy. In other words, I find it extremely easy to shoot well in both slow and rapid-fire. This is akin to how "good" a gun feels and is subjective but it would appear that from the gun's long service history and relative popularity among 9mm shooters, a great many folks feel the same way.
No other 9mm pistol feels quite as "right" to me as the Hi Power. For me, this pistol groups plenty tight enough for my purposes and is easy to shoot accurately at speed as well as in slow-fire.
It has been reported that some 9mm pistols suffer reliability problems when using 147-gr. JHP ammunition. While I admit not being a user of this weight bullet in 9mm, I have had no problems with the limited amounts that I've tried in a couple of Mk III pistols. Ammunition used was Speer Gold Dot, Remington Golden Sabers, Winchester Silvertip, and Winchester Ranger. These loads ran smoothly and w/o malfunction using either the standard factory 17-lb. recoil spring or the Wolff 18.5-lb. All of this ammunition grouped well with ejection being positive. People considering the Hi Power but preferring the "heavy bullet" approach should have no reliability problems based on what I've seen. (This does not mean that the ammo to be used shouldn't be tested in the individual pistol.)
Spare & Aftermarket Parts: Parts remain plentiful for the Hi Power from the manufacturer as well as from Cylinder & Slide and a few other places. There will probably never be as many aftermarket parts and choices as exist for the Hi Power and Glock pistols, but spare parts are available and should be for years to come even if FN does eventually cease production of the Hi Power.
9mm Cartridge: I like it and consider it the "perfect" cartridge for the sleek Hi Power. There are other articles on this site focusing on various standard velocity and +P rated 9mm loads for the Hi Power so I won't dwell deeply on it here other than to say that the choice is wide for people interested in high-performance loads in this caliber. With the advent of some of today's bullet designs I think the "gap" between standard velocity performance and that from some +P has considerably narrowed. I do not consider the 9mm wanting in terms of performance when loaded with such ammunition as Winchester's 127-gr. +P+, Corbon DPX 115-gr. +P, Remington's 124-gr. Golden Sabers in either standard velocity or +P or Speer's 124-gr. Gold Dots in either pressure range. The old Federal 115-gr. JHP isn't bad, either! While I do believe that in its better loadings .45 ACP edges higher performance-wise than 9mm, I am not convinced that the difference is significant. I am sure that it is not if the larger caliber cannot be shot as accurately as the 9mm. In short, I'm quite happy if armed with a 9mm Hi Power and what I consider good defensive ammunition.
Conclusion: The FN Hi Power, GP, P-35, or by whatever name it is known has served people going into dangerous situations very well for many decades. Though its popularity is declining in current times, the pistol remains a favorite of many handgun enthusiasts and will for decades to come. I think I might have written many of the reasons why. Born in a different era, some consider it a relic. Others simply see it as continuing to do what a pistol should: function reliably and allow the shooter to put the holes where he wants them. I see it as something a little different. To me it is a reliable design but one that is also a work of art, combining function with graceful lines and deadly beauty.
For those desiring to do so the Hi Power lends itself to custom touches and a number of famous gunsmiths specialize in Hi Power customization.
I have no quarrels with those opting for a different 9mm. Each of us must "work out our own salvation" so to speak, but for myself, no other 9mm satisfies so completely as the Hi Power.