Mike , welcome to the forum. I have held and shot a P3AT and the Kel-Tec is more of a Yugo to me, I own a Ruger LCP it is a refined and improved P3AT and carrys very nice in the pocket but is still a 380. I owned a 340 SS like Ktrains 340PD only with a stainless cylinder and 1oz more weight, firing full power 357 mags from it had a very sharp recoil and I don't think many would fire 50rds in one range trip. The R9s is a little thicker than the LCP and the LCP loaded weighs 12oz, the R9 weighs 12.8 empty. Recoil of the R9 to me is not much worse than the LCP but a little different, and the wider backstrap spreads it out.
As to the premium ammom, I have fired WWB and Remington UMC and had no problems with either, each R9 seems to have it's own preference as to ammo diet.
For a pocket carry gun I dont think you can beat the R9, and
quality is first rate along with customer service from the factory.
John