Is there any "blow back" into the face of the shooter? From experience, some ARs and FNCs will have some gas leaked back into the shooters face from the extra gas pressure dwell during the action cycling. Does the PS-90 (or the Five-Seven) do this?
Looking at the systems (ive got a FNC with suppressor) I would say its less likely to get alot of gasses in the face with the PS90, assuming a good magseal. Its easier for the gasses to go downward, so they probably will.