I installed the 10149 build on my M8 which previously had Windows 8.1.1 on it. Once I installed, I opted to not restore from a backup, but to start from scratch. I really only care about my calendar, contacts, and photos, so no big deal. My M8 was initially hot after the update, but cooled down to normal after a while and never heated back up. I think it was mostly due to the phone downloading updates to software. I updated this past Saturday and have been using the phone since then with only a few minor problems. I don't get real email notifications although other notifications seem to work as normal, and the phone has restarted itself twice since the update. I'd say pretty stable for a pre-release piece of software.