FYI Duff; Neither the Flex or Rupes DA's backing Plates can be interchanged with a PC, Megs or GG DA. The Flex and the Rupes have their own specific backing plates. The PC, GG or Megs backing plates are interchangable
IMO BOTH the Flex and the Rupes are the TOP DOGS in the DA place. That being said, if I had a choice it would be the Flex. It is the only Forced rotational DA on the market. All others are free floating DA's.
The Backing plates for the Flex makes it a more versatile machine than the Rupes. I have the Flex and the PC and since I have the Flex, I have not used my PC for quite a while. If I do it is for waxing or using a 3" pad with the 2 7/8" backing Plates.
The Flex cost less and is a workhorse and more versatile than a Rupes. The Rupes, IMO is the BEST free floating DA out on the market today.
Either way you can't go wrong. Look at all the Flex vs Rupes threads (there are many) and hopefully, that will help make your decision.