1K,
I'm a former PM9 owner who now carries a J-Frame. What it came down to for me:
1) The PM9 is smaller in size, but it weighs more. In the case of pocket carry, weight= printing. However, it was awesome for tuckable IWB carry.
2) I could never get my Kahr to run 100%. After the break in was over I had a few trouble-free range sessions, including my defensive loads. One night I used my PM9 to dispatch a deer that I'd hit with car. The round failed to eject. A huge deal? Not in the grander scheme, but I was hoping for better.
The 340, on the other hand, has been trouble free. I'd highly recommend one to anyone who's not married to 9mm for pocket carry. It's light, easy to carry in a variety of ways (IWB, Pocket, Ankle). I also like having the ability to fire .357 Mag or .38 Special, though I'll warn you that full throttle .357 rounds are a little rough on the hands of most shooters. Speer makes a "short barrel" GDHP round that I've found to be a reasonable compromise in power and recoil control.