I have both the 7424xp (xact fitting backing plate with LC HT 5.5" pads) & the Flex 3401 with LC interchangeable bp w/5" hybrid pad system. Two entirely different machines which I use on every detail. The FLEX is terrific and my go to unit,especially for compounding. I even like it for applying wax because I can set the speed at 1.5 and the blue finishing pads always turns.

rops: Personally I think the Flex and PC complement each other (DA & Forced Rotation) whereas the Rupes and PC are more redundant. (both are DAs) Either way you won't make a mistake but having tried the Rupes, I would still pick the Flex - YMMV. Remember, ask 5 detailers a question and you'll get 6 different answers.