I used to own a KT P40, not a conversion. What a piece of crap. This had to be the most unreliable, uncomfortable, and PITA firearm I have ever owned. I knew getting this pistol that it would be a beast to fire, .40 S&W in that small a package definitely packs a wallop. However, with the 4 magazines I had I never once had it completely go through a magazine without jamming, even with taking them apart cleaning and reassembly. The 3 smiths that looked at it couldn't find anything wrong, and the 3 instructors that looked over my stance and grip told me it wasn't limp-wristing. Since this was to be my CCW piece, I knew that I couldn't rely on it.
I sold it, with the message that it had issues with reliability. Person that bought it was ecstatic that he had found one, turns out he collected Kel-Tecs.
IMHO, stay away from the KT P40. It's a good idea that wasn't executed well at all. Their more recent products like the PF-9 and the P3AT are good examples of good ideas followed by decent execution. I think every company makes a lemon of a firearm now and then and the P-40 was Kel-Tec's.