I have been looking at the Surfire lights and darn if I am at a loss to understand the differences between them - their web site does not allow for a side-by-side comparison as I would expect.

About the only thing I see are the 900s use a throw lever type of mount and the 910s use dual thumbscrews. The As have the small reflector and the ABs use the larger 2.5" Turbohead reflector for longer range applications.

What else am I missing? Any users out there - I am looking for a unit used for home defense.

Well, you don't seem to be getting a lot of help.  I'll give a little,,, the 900 has the release lever to attach/remove.. the 910 attaches with bolts.  I can't help with the A-B thing

Ive got the thumbscrew one...its really really heavy compared to other lights I looked at.  However, I LOVE it, and cant find anything I like better.

ETA: Saw your looking for a HD weapon - get it. I've got mine on my 10.5 SBR, and it handles fantasticly.

height=8

Quoted: About the only thing I see are the 900s use a throw lever type of mount and the 910s use dual thumbscrews. The As have the small reflector and the ABs use the larger 2.5" Turbohead reflector for longer range applications.

That's actually a really good summary of the differences - that's pretty much all there is to it.

Quoted: You've already nailed down the mount differences, the dual thumbscrew mount is the stronger of the two but you should periodically check to make sure everything is tight.

Loctite is your friend.

get the Larue replacement mount.  As it has been said many times if Larue is an option go LaRue