As a former owner of several SVS, Paradigm, Velodyne, JL and DIY subs, I have to say that I am really pleased with my in-ceiling sub from RBH. It doesn't dig nearly as deep as most other subs that I have had but it's just pretty darn good if you have to have a sub that can't be seen at all.
The only issue I have noticed so far is since changing from Paradigm Studio 100"s to inceilings, I have to use a pretty high crossover so I do get some localization from the sub and I can tell that it is on the left side of my room. I am about 99% certain that a second one will be coming after we complete the home remodel project which should even things out.