Junebug sorry to hear about your sciatic nerve problem. Havent had that happen to me but I hear its really painful - but fixable with time off and alot of muscle relaxers, and possibly steroid injections, and rehab programs.
Too bad you want to get rid of the Flex, but I have one too, and I can see why you would want to not have to deal with it.
I started out using a Rotary way more decades ago than I can remember, then started back up a few years ago with the PC7424, the Flex VRG3401 like yours, and recently got a Makita 9227, and have to say that for smoothness, the Makita has it way over the other two machines, and of course, as you know, its faster at correction, but has its own sets of challenges, because it is a rotary.
I am using it all the time, in both 6" and 4" configurations, and loving it more and more all the time.
I know the Cyclo has been around for at least 30 years or more and many old school detailers swear by them. They do alot of things besides buffing, including brushing, sanding etc., and have lots of accessories you can buy for them.
They seem to be louder than a PC or the Flex and have alot of looks like vibration, so that may or may not be good for your condition either...
In any event, hope your get better soon, we will keep you in our prayers..
DanF