There are a few tailcap switches floating around; I have a few and am not crazy about any of them to be honest. For an incan MM, I always return to the stock twist mechanism. No, the mineral glass is similar, but not the same as a UCL. The UCL has 99% light transmission through it; lets more lumens out. The TT1L bulb is brighter than the nexstar bulb, as it draws more current (1A, IIRC). Not sure about the bit size, I just tried a few until I got the right one. So far, the 1L/MM combo works fine for me. I don't like the beam artifacts, which is why I got the LDF (light diffusing film) on my UCL lens. Converts it to a very floody beam, which I like for this light.