I've owned a bunch from Rel the older Studio 3, S/3, S/5, Rythmik FG12, SVS SB3000. I owned the Rythmik and SVS side by side. I thought the Rythmik maybe had a slight edge. Fast forward a few years and had a system with a sub again I checked Rythmik and they just had nothing on hand. I ended up with the SVS SB3000. Awesome sub, easy to use and adjust with phone app, zero complaints.
The Rels I owned never went deep enough for my tastes. I find Rel to be like Bose, not a knock on sound or quality but a king of marketing- they're on it, maybe the best. I think that's where a portion of the cost goes instead of building a sub that can hit a solid 20hz. Just my experience.