The "2" series of Aimpoint Comps are the current production models of these sights, as in Comp M[b]2[/b] (night vision compatible model) and ML[b]2[/b].
The biggest difference between the older M and ML and the current M2 and ML2 is the extended battery life of the "2" series, which is now from 1,000 to 10,000 hours, depending on intensity setting.
Here's the specifications on the M2, from Aimpoint's website:
[url]www.aimpoint.com/products/compm2/speccompm2.htm[/url]
There are other improvements that I'm sure will be pointed out shortly.
Chris