Rythmik are great subs that I've heard in numerous systems/ rooms. Doesn't mean they are for everyone or that a single sub heard once was set up well. I know someone struggling to get bass in his room trying different subs, up to 4 subs, room treatments, modifying room, and experimenting now with room correction, and still currently struggling.
Despite hearing the Rythmiks match up well with my very articulate and natural sounding Daedalus speakers, I decided to order a pair of Daedalus passive subs with Daedalus external crossover. I will definitely keep the Rythmiks for another system, but am anticipating being very impressed with Daedalus BOW subs. I try to buy used when I can like I did with my Daedalus speakers, but never see these up for sale used. Doesn't hurt that when looking for WAF for dual subs that you are getting beautiful real hard wood finished to your specifications.