I'm using a Brinkmann Maxfire LX with a Q5 drop-in on both my HD shotgun and my AK. Works great both indoors and out.
As far as how to mount it, it really just depends on what's comfortable for you. I've got a tri-barrel mount on my shotgun that places the tailswitch right in front of my support-hand index finger. It's very easy to flash on with the momentary, and then can be clicked all the way in for constant-on. I feel more comfortable with this setup than with the tape-switch setup I had before.