I like the LB on bellows or tubes. The only real problem is that of adjusting the sweet spot. I generally end up just leaving it in the middle. As you know, with macro it is hard enough to get the focus correct handheld anyway. Trying to handhold, find a focus spot, maintain it, and go for a sweet spot all at the same time are just too much for me.
I'd really like to have a Composer for doing this sort of thing, as well as for long exposure shots.
Pentax K20D
Lens Baby 2.0 @ f2
Yokohama's Minato Mirai area at 4:30 a.m.