The P7M8 more so than the PSP and then the P7M13 even more rare than both. None of them are terribly "rare" per se, just harder to find than others...plus, it is an "H und K" and there's a price tag with that as well.
I had the exact same experience. It did nothing for me and I could not hit squat with it....not to mention that after about 50 rounds it became nearly unshootable due to the heat coming off the piston into the trigger guard. I traded mine off and didn't feel bad in the least.
Problem with the encore when shooting suppressed is that every round will have first round pop due to the time involved in manipulating a breech loading action.