Re: Why the T-1 over the Comp M2
The T-1 is going to have a longer battery life, and will be easier to mount, taking up less of a rail foot print. It is physically smaller and lighter. The batteries are much easier to find, and are less expensive.
I think the switch on the T-1 is less prone to accidentally turning onto it's full-on battery-killing position. It is small, compact, and tough. What's not to like?
The comp M3 will have a similar battery life (much greater than the M2). The M series have a bigger tube, which when shooting in awkward positions, can be a good thing.
I'd like to try out a T-1 long term (have shot with them a few times, but don't have one of my own). I am thrilled with the PROs we issue at my department - they are solid and about as problem-free as I had heard.
You can't go wrong with either.