Sounds like a nightmare. Plus it's a Smith semi so it's probably going to feel like garbage in the hand and have a terrible trigger.
I have enjoyed the M&P 9. Definitely would not want it in a worse cartridge though.
Everyone says the trigger is subpar on them, but I guess I'm just not picky on that point.
The real problem with 5.7 is that it really doesn't do anything special in a handgun. 9mm works well enough for most all of the 5.7 handgun duties. 10mm covers the "9mm but more" role for half the cost. The 5.7 makes some sense in a submachine-gun/PDW role, but there are very few people for whom that is applicable.
IMO it's way overrated even for that, the ballistics fucking suck after it's spent most of its energy making its way through Lv.IIIA armor, people who have used the P90 in combat attest that the 50rd magazines are critical because you'll need to put long bursts on target to get any reasonable effect. A shorty Mk.18 carbine has far greater power and range, and uses commonly available ammunition and magazines, it has slightly less capacity and it's blasty as a fucker, but you don't need even close to as many shots, and I'll take loud over piddly if my life may depend on it.
I think that the only great part is the form factor of the P90, which is nicely compact and high capacity, but something better could be devised with a better cartridge which fits a similar envelope.
5.7mm feels like it could be a good varmint cartridge, like a better .22WMR, and like it could be fun for plinking, but it'll just never win over or compare to rimfire. For high capacity and a small bore, I'd be more interested in a Calico M100, I would only really need one, maybe two magazines, and .22LR is fairly zippy from a rifle barrel, more than enough to control the varmints. All the varmints.
Goldeneye 64 and Stargate SG-1 nostalgia isn't enough to hold up the P90 for me, Stargate Command should have issued M4A1s with red dots and some nice heavy barrels with fluting.
But I've always been interested in what something like an M1 carbine could do with the 5.7, mostly because PS-90s are gay.
That was a thing before the P90, see the earlier discussed .22 Spitfire / 5.7mm Johnson, essentially a far more powerful 5.7x28mm but with a much worse magazine.
