I have the Bad Boy and the Butt Boy.
The horseshoe-shape of the Bad Boy makes it really awkward to try to fit inside the body properly, whereas the L-shape of the Butt Boy makes it much easier to insert.
The vibrations are equally mediocre in both, as the bullet isn't that powerful, only has one setting, and fits inside the portion of the toy which remains outside the body.
If I were you then I'd consider the Fun Factory Duke
instead, or the Lelo Billy
if you're willing to spend a little more.