They do act very much the same as tey increase fuel pressure by restricting the amount of fuel that is allowed to return to the tank, only the FMU uses a boost reference to raise full pressure by predetermined amounts via the disc that is in it, example 4:1, 6:1 etc meaning that for every 1 lb of boost it sees it will increase FP by 4, or 6 respectively. The FPR has a much smaller range of adjustment as it relies on vacuum and not boost to alter the FP, it is set to run its max pressure when vacuum is at its lowest (full throttle) and it runs at a decreased pressure when it is under vacuum.