I have an Ultra-X12 that has replaced my LFM-1 Plus. I love it and I'm quite happy with my decision to replace the Plus. The bass response, I find, is very tight and precise. I also have it on hardwood flooring using the spikes/discs, but haven't experienced any "loading" or undesirable muddiness.

Since introducing it into my system several months ago, I've enjoyed an improved listening experience from what I had with my previous sub.

One example...
Playing "Edge of Tomorrow's" opening scene, which contains some extremely low bass, demonstrates to me the X-12 can reproduce accurate, precise bass at these low levels and every desired frequency above those.
Just my 0.2¢.