I went with a BB400 in a MiniMag, using the stock twist-on/off control, with no problems. From what I can tell, there is no visible damage so far on the Luxeon emitter or the optics from the constant twisting and contact, and (at least in my setup) there is zero risk of crushing the module by twisting the head on all the way. The threads bottom out on the barrel, in fact. This may be different, due to manufacturing tolerances, AA type, length, etc. so double-check it before you do anything. I didn't want to have to use the Kroll switch because of known problems, added length, not able to fit (very well) in stock nylon holster, can not use in candle mode, etc.
I chose a MiniMag host because they are quite common (I have some 5 of them), looks like a normal (read: DIM!) MiniMag until you turn it on (!) and so then I can get a great reaction out of someone when I hand it to them. /ubbthreads/images/graemlins/bowdown.gif
A BB400 with a Q3L upgrade should be waiting on my doorstep tomorrow evening. /ubbthreads/images/graemlins/grin.gif