I have a Sub 9 in 9mm for several years, and it's great. It is the better gun, but it cost more than twice what the Sub 2000 costs.
I just got a Sub 2000 in .40SW and have a few comments.
There's a lot of casting flashing that needs smoothed down. Plan on spending a half hour with a pocket knife rounding stuff off.
I strongly suggest getting the butt extension from Kel-Tec as it will act as a guide when folding (eh, you'd have to have one in hand to see why). If you don't want to, then open the slot in the back of the front sight so it will catch the detent bolt. You want a broad, shallow "V". You can also file the sides of the detent bolt so it catches the guide slot better.
It needs a bit of work to make it easier to open/close and to improve the trigger, which is a bit nasty. The machine screws holding it together look like they are all 1/4" 8x32. I just replaced the two on the hinge with a couple 1/2" long to see if they will but into each other inside the pivot, Looks good so far, they might just do it. Might need to replace one with a cut down 3/4" screw or drop some trash between them to hold them just a tiny bit further apart.
Getting to the trigger is a bit of work. Go to KTOG for information on getting to it, there's tricks to putting the rifle back together or it will drive you nuts:
http://www.ktog.org/The manufacturer's web site is:
http://www.kel-tec-cnc.com/The web site without the "cnc" in the URL is one of those parasitic sites that makes money on people making mistakes.
There's several other groups and sites dedicated to the Sub 9 and Sub 2000, worth visiting to see what they have to say.