Martens,
I have a Tac holster that allows me to carry the M3 mounted on my pistol, but my Class A uniform I have to carry it on my belt on a slip on type holder. It's cool as I have got used to putting it on, and taking it off quickly.
Have you found that the only draw back (if you can call it that) is when you draw down on someone with your light on, and mounted, they can't see that they had better comply or else loose their...................? Well lets go on shall we?
No I do like the handsfree weapons light, especially when you are doing a building search and you don't know who/what's there.