By the way I have only tried the Xotic RC boost, but I did not care for it at all. It gave a hard, steely solid state feel and sound, especially in the high end. IMMO, YMMV etc etc.
There's a little bit of that with the BB that I have as well, though I don't mind because it seems to work well in the context of my recording work, when I often want to create a different feel than the tube amp gives me.
In fact, I really like the BB. It's one of those things that's just gonna sound the way it sounds, and it can't be dialed out.
Funny how we both tend to notice a departure from pure tube sound so often regarding many pieces of gear..