How stable is OS2 beta 3?

You need access to the developer portal to get access to the watch beta. There is no watch public beta. If your phone is on public beta I assume you do not have the access needed.

Generally, I would suggest waiting on the watch update unless you need it for testing. You can't go backwards like you can with the phone so if it stinks for you you would have to wait until it's better. The few new features are not really worth the effort yet for the watch.

 

Beta 1 and 2 where pure sh/t, freezes, 3 hour battery life and so one.

Beta 3 is in another ballpark. The battery drain is gone and it does not freezes anymore.

If you really like to try new betas it's good to go. Only if you ask me: don't do it. It's just not new enough for it. The only thing you can use now are the new clock faces and the Night stand. Not really worth the risk beta 4 is sh/t again.

If you still want to. You only need a phone on 9.0, so if you are on Public beta you are good to go. The watch does not need a developer registration like a iPad/iPhone does on closed beta. So be creative and download the profile "somewhere else"