I have a poly Kahr P9 and I LOVE it for daily carry. Got rid of my Glock and replaced it with the Kahr. My P9 has been 100% since the first shot, and I'm over 1200 now without a single problem. Super accurate, super light, super THIN.
I'd do more research on the P40 if I were you before I dove in. The Kahr P40 seems to have more issues than any other Kahr pistol. Maybe it's just too much gun for the size/construction. The steel K40 is great but I wouldn't buy the polymer 40 until they get the bugs worked out.