Very happy with Rythmik. Purchased very easily and with great communication via Ascend Acoustics. I also have a REL, which I like.
If I had to choose between them, I prefer the Rythmik to the REL. In my opinion, there is a lot to do to make subs work smoothly in a room. The lack of adjustable phase all but a few expensive models of REL make the Rythmik much much easier to dial in. They have other adjustable features, too, which the REL lack. The fact that they are servo controlled also impresses some folks, but I don't know enough to say that that particular engineering difference from the REL is an advantage.