I don't own any, but have handled them. A couple buddies have them.
My co-worker/shooting friend has the Sub-2000 9mm Carbine. I've detailed in this forum before, my utter disgust at this abomination of a firearm. It makes my Hi-Point Carbine look good! Nuff said.
My other buddy has the compact .380 pistol. The trigger is stiffer than I prefer, and it's mighty small for my big mitts, but it functions well. It would make a very good concealed carry gun, or a hide-out piece.
He also has the .223 caliber SU-16 rifle. That's a nifty gun, in the same basic price range as the Ruger Mini-14. Decent accuracy (though it needs the optional adjustable rear sight!), and it has been 100% reliable. Uses GI AR-15 magazines too. Scope mounting is easy, as it folds under. They got that bit right, unlike the Sub-2000. Light, handles well, is stouter than it looks - not flimsy at all.
Well, that is my experience with the Kel-Tecs.