I recently got dual Rythmik F12Gs for my stereo setup. Before this, I had no first hand experience of owning subs. If you like subtle, sophisticated, unobtrusive, well-behaved bass coming out of subs and want your subs only/mostly for stereo music and not so much for home theatre stuff, I can recommend this model. I chose this over the REL T9i. REL is constructed like a thousand bucks and seemed to have more powerful bass, but when it comes to clean sound, seamless integration of subs into the room, Rythmik walked all over it. I have had friends who have visited me and were completely unaware that 2 subs were working in the room, but when I turned off the subs, that is when they realised how much the subs were adding to the overall heft of the mid-bass/sub-bass regions of the spectrum and how incomplete the music listening experience seemed.
For HT usage, I would probably say REL was more authoritative than the Rythmik F12G but then the G model uses a paper cone. There are many differences actually. Anyway, I am really appreciating the direct servo technology of the Rythmik. YMMV.