Does this sight have auto-shut off?

even though it boasts a 50,000 hr. battery life you would be under the impression but it DOES NOT. It is a well made sight, and I am pleased with mine so far but if you must have you weapon in an "ready" state at all times this might not be the option for you.

Since the mount has been reported to break, is this compatible with any other more reliable mounting systems?

I have one on a 50 Beowulf AR-15. I've put well over 200 rounds down range and the mount seems to be good as new. Since the mount is a standard picatinny rail you should be able to find one the same height and use that. I'm not sure if you can find one that features the co-witness option though.

Is this sight parallax-free?

Short answer: yes. Nothing is 100% parallax free. EO Tech has been proven to be the closest. I have multiple red dots spanning a wide variety of price points. The AT3 is by far the most economical red dot that is still considered “parallax free”. This is a very good optic for the money. Probably the best “bang for your buck” available.