Well, I started with the FiveseveN about two years ago and invested considerable time into working up an assortment of usable loads for it. Factory American Eagle and SS197SR is loaded quite mild, and while the American Eagle at least comes with a FMJ bullet, over the years they've rounded the nose more and more to insure it won't make it through body armor. The polymer-tipped, mostly hollow-core V-max type bullets are not really ideal for large game, which is the same size as humans. With hand loads the 5.7x28 can easily be pushed fast - pretty much on par with the .22 TCM factory load, but hand loading the 5.7x28 is beyond what I would recommend for anyone below the level of "expert" to load ammo for. There are just so many aspects that must be known and understood, along with attention to detail. If I were going to set up a semi-automated 5.7 loading machine, I would make it dedicated only to the 5.7, never to be altered or swapped out with conventional calibers.
The BEST way to get performance ammo for the 5.7 if you can't afford to pay someone else $3 or more per shot to make it for you, is start with American Eagle when you can find it cheap - like $16/box, pull the bullets, then reload the new cases with your performance powder charge and either re-cap with the factory 40 grain FMJ, or consider the Speer 40 grain Spire point as a REAL SD/combat load. I know it doesn't look as cool as the long, shapely V-max, or the Barnes 36 grain, but it's built for business with a dense, lead core, thick jacket, and sharply tapered nose to a tiny exposed lead tip. Loaded to 2,000 fps the Speer SP will bust through 3/16" steel plate like it's not there. It's also going to hold together going through organic material and has the density to shatter the largest bone. The 40 grain Speer has a decent enough B.C. so that when zero'd dead on at 9 yards, the bullet will never rise more than 2.5" above LOS, dropping to around 3" below LOS at 150 yards, at which point it's still supersonic.
Another bullet I intend to work up is the Speer 33 grain Hornet JHP. This little gem has a short bearing surface and dense core and should be capable of exceeding 2,200 fps in the FiveseveN without straining. This would be an excellent high shock load inside 50 yards, with steel penetrating ability.
As to what one might use a FiveseveN for? SD carry of course! That is what it was designed for. It weighs close to nothing, holds a solid 21 shots and has high functional reliability. Yes, it's large, but being single-action, the grip reach is doable for most. The location of the safety seems to vex and confuse many, though it's quite instinctive and easily adapted too, BECAUSE it's quite instinctive. The safety lever is right at the shooting index finger and easily snicked on or off without altering the grip. Naturally the FiveseveN has the expected firing pin block, and magazine disconnect. I have carried mine in all sorts of ways, generally in a small carry bag with half a dozen 20 round mags as a "car gun" and at other times SOB, and even front pants pocket, and yes it WILL fit if you have large enough pockets!
I think the 5.7x28 is the most innovative antipersonnel cartridge to come along in a LONG time and it has a well-documented track record as to its effectiveness. The round does its thing due to high velocity combined with a small, lightweight bullet that tends to create non-linear wounding. It doesn't have a lot of brute force - kinetic energy, but for it's intended role this is not needed. As for carrying one in the field against animals....thin-skinned animals such as large cats - absolutely - with the right bullets and uprated velocity. Against two-legged predators - absolutely. Against bears, not likely, though a serious shooter with the nerve, could very likely punch holes through a bear's skull, but it wouldn't be my first choice. That's why I have a G460R Longslide.
The big negative for the Fiveseven is that if and when FN stops making the cartridge it's gone. There aren't any other cases from which one can readily form 5.7 brass...it might be doable, but it would require a lot of forming and turning, and fire-forming, so that means it's gone when the maker stops supporting it. Due to the expense of the gun, it will never achieve wide market penetration, and of course, aftermarket anything for the FiveseveN has become the playground of those with more money than time. Like $500 barrels, and $60 a box custom ammo, and $80 aluminum triggers.
About six months ago I finally jumped into the .22TCM pool, only in California that meant the .22TCM9R end of the pool which started out a YUGE disappointment, but has morphed into an amazing little cartridge!
But, as is, the .22TCM factory load is quite good. A 40 grain, JHP leaving a 5" barrel at well over 2,000 fps and close to 400 lb-ft of KE is serious business, no hand loading needed! Where the .22TCM9R is available the same holds true for 9mm size pistols...a LOT of speed from a very compact gun. My Glock 19 with 4.02" TCM barrel will hold 16 - 33 shots and is as light as the FiveseveN while being nearly half the size! It also has FAR superior ergonomics and enjoys all those good things available to all Glocks. Even with the extremely limited versatility of being able to accept only a single factory load from Armscor, it's a worthy SD cartridge.