In my experience an RX doesn't particularly speed up the carpet cleaning, it can actually be slower than a wand in some cases but can help get the grottier ones cleaner more easily. I'd say it is slightly less fatiguing on big jobs, although I always seem to end up with terrible arm ache in just one arm.
The jury's still out with me as to whether it is the answer to my prayers for big commercial jobs.
The hard floor attachment is a polyprop scrub brush the same as you'd get on a rotary. But it sprays and extracts through the bristles. It's a bit Heath Robinson - the vac pick-up is just a couple of open-ended pipes sticking through the brush!
I haven't bothered getting one and don't think I will. The best way of cleaning tile & grout is to scrub with a pad on a normal rotary, dwell for a decent time, and then rinse off. The RX hard floor head is very limited in its uses. I tested it out on a patch of warehouse floor (powerfloated concrete) and for that sort of thing, an all in one flood/scrub/rinse process yes it could do a service.
But you couldn't do any vinyl floors with it, or anything that needs a proper scrub like with a black pad. The agitation of the brush just doesn't get anywhere near the same level of scrubbing power as a black pad!
Just my experiences.