I have, and didn't like it. It's well-made, but not for me. I don't think it came anywhere close to comparing with my 2 Pedullas, my Alembic, my full-on custom Brubaker, or my Modulus. It just felt big and uncomfortable to me, has a giant neck that just wasn't for me. Well, maybe the neck is better than my Alembic, because that thing was like a log. I don't recall what the BTB sounded like, I was so put off by the way it played. But am very happy you like them.
If you don't own one... I think I don't understand... The SRs are rather the opposite of the BTBs, they are so small. Both are well built.
IME 19mm is the domain of 4-string basses. But I like 18mm anyway. Just feels more comfy.
I like the SR models and I don't, which is interesting as I just bought one. The necks feel very small, but I am in love with the light weight Ibanez if putting out.
Not sure what music the OP wants to play, cause it kind of matters. I can't see a BTB fitting in a rock band.