I've got one. They are a blast to shoot - but really REALLY loud.
Definitely need the handguard that KT sells, and their muzzle brake is supposed to tame the muzzle flip. Might google for kel tec forums, as there are a few good ones out there that discuss this and others (PM me for details).
I haven't had a real good chance to sight mine in, the factory sights leave much to be desired. Others have reported good results. I've tried a couple of red-dot optics, but may have to try my Eotech on there.
Its not recommended to shoot Wolf or other ammo out of them.
It is a niche weapon, if you have an AR - the mags will work which is nice - flexibility.
The only drawback is it gets expensive to shoot
And you can't put a vertical foregrip on there without the ATF paperwork.