I have been using Window 10 Mobile Preview on my Lumia 1520 for about 1 month. It is really buggy, but I don't have a PC to roll back, I am on a mac. So I deal with it. The battery drain is pretty bad, the apps crash and the phone runs really hot. That being said, I do like the layout and the potential of the new OS more than 8.1. Just not ready for primetime. Still hoping for a fast ring release this week to improve stability.