They do tend to sit offset to the right on a the rail though. Not that critical as you can get them to sight in at 50 and 100 yards without too much trouble. I guess the 1913 rail is a little wider than the weaver!?
I do like this "G2" model a little better than a MkIII. The MkIII followed next in line. The G2 is easy on and easy off by rolling the power switch "on" or "off" with the weak hand and it faces the shooter, so it is at the back of the unit. The MkIII has the somewhat problematic photo sensitive eye that is also the on-off switch. It is a smaller switch and you turn it through a 90 degree arc to tun it on. It is at the front of the unit away from the shooter, so you experience just a tad less positivity in activating the unit. On mine, the red dot does not adjust with light levels, so I guess the "eye" part no longer works, but the unit itself still lights.
Yes, stripping down a 123 will work great in this unit. What I did find that was odd though, is the battery goes in backwards from how the DL 1/3Ns are indicated to be installed. Can't figure that one out? Just don't panic if you strip the plastic coating off a Surefire or Duracell 123 and then load it up and turn the switch. I thought my unit was kaput, but just for giggles, I turned the battery around and low and behold, light!
Old school guy in a new school world. :-)