They're lightweight, use common pistol mags, very easy to store with how they fold up. Chances are you're going to want to get the stock extension from Kel-Tec, since the LOP is VERY short out of box.
There's no easy way to mount optics on the carbine, which is a bit of a drawback to some (including myself), but the iron sights are easy to see, darned simple to use, and mine were dead on right out of the box, all the way out to 100 yards (a little kentucky windage was necessary, but they weren't hard shots by any means).
Now, you can't use aluminum cased ammunition (or at least REALLY REALLY shouldn't. It was even on the Kel Tec website, and I believe it's in the manual), but other than that, it's been very reliable, with a few very specific exceptions in my experience.
It jammed pretty consistently when using a 33rd Glock magazine loaded with PMC 115gr FMJs. I think that was more a case of the magazine not liking the ammo, more than it was the gun not liking the ammo, as that combination of magazine and ammo jammed in my Glock 17L as well. The 17 rounders worked fine, and the 33 rounders have yet to jam with Georgia Arms 124gr FMJ.
All in all, it's one of my favorite weapons, and I consider it more than just a range toy. In fact, if my HD shotgun were ever in the shop for repairs, I'd grab the Sub-2000 and park it next to my nightstand without hesitation. Loaded with 147gr GDHPs of course.