Coincidentally, we've just gotten a few PROs in for some of our patrol rifles. Initial impression is that it's a nice optic, albeit a tad large and heavy for an M-4, but some of our guys (and gals) seem to think they're shooting better on the qualification than they would with iron sights.
On a side note, our EOTECHs, some of which are pretty old (mostly 512s and 511s) are holding up well, with only the usual issue of battery replacement. My personal 512, which is probably almost 10 years old now, still performs exceptionally well, holds zero wonderfully, and so far, I prefer the EOTECH HWS system to the PRO.
I'm not gonna replace a perfectly reliable optic that works well for me at this point. As far as its tolerances for extreme temperatures, it's been to classes in the Arizona desert, spent time in the Eastern Washington desert (shot much in temps over 100 degrees F), and shot quite a bit in the winter months at our cabin in the Cascades ...
For the earlier poster who noted Pat Rogers comments on EOTECH -- his prejudices are well-known and can be taken with a grain of salt. Though he's spot on about students who don't know how to maintain or use their gear, so ...