I can tell you that the FFM does push your lower jaw back and it irritated my TMJ when starting out, but my jaw muscles are slowly acclimating to it.
I run a Remstar Plus now too. The Remstar Plus is not real smart in the pressure department I check mine often with a digital manometer and a tee fitting I made up from hardware store / automotive parts.
I always run a pressure check when I switch masks though because I have found that the exhaust vents are different on each mask (some are less restrictive than others)
If I use the FullLife and set the machine at 14.5 cwp, I get a measured 15.9 cwp. Quite a difference!
If you are interested in doing your own pressure measurements to spot check your equipment, just give me a buzz and I'll show you how I use it all.