I'm not a great fan of Kel-Tec, and have handled a few of their guns.
A friend has the compact 9mm pistol, and let me put it thru it's paces. Not a bad "carry piece". Light, accurate and worked okay in my big hands, though my pinly finger was left hanging. 100% reliable. My only real gripe was the very stiff trigger - but then, in a high-energy situation, I'd have no problem using it. You don't want a very light trigger when the crap hits the fan.
The Sub2000 carbine was much less than I'd hoped for. Since it's designed to fold, it's difficult to attach a scope or optical sight - which it direly needs, given the utterly horrid, virtually useless "sights" on it. At close range, point-shooting, it may be of use. My buddy's Sub2000 uses the plastic Glrock magazines - they can be hard to load the last couple rounds in. He should've gotten it with the magwell to use Beretta mags - he has a Taurus and the weapon could be tweaked to use the Taurus mags easily.
The "stock" was way too short - I'm 6'4" with the arms of a Greyback Gorilla - and I could barely operate the contraption. Even my buddy, being a short little guy, admitted it was short for him too.
With that being said, he could shoot some fairly good groups with it at 50 yards. It seemed very reliable too - never balked with UMC, Winchester or his hand-loads.
Some folks like the SUB2000, but it just wasn't good for me.
I haven't seen or handled the new .223 folding rifle yet, though I'd like to.