I wouldn't recommend it, there still a lot to do and I doubt that any developer working on 5.7 will spend much time or thoughts on upgrading from 5.7b1 to 5.7final. Maybe if you're code savvy, but we've got lots of c5 know-how and don't intend to work with 5.7 right now..

You should take a look at a similar discussionhttps://www.concrete5.org/community/forums/5-7-discussion/upgrading-... (linking to franz's answer).

Also wouldn't recommend trying to put content together on a 5.7 site just yet, there are still bugs which may lead to database inconsistencies and could end up being a pain to try and fix. However, if you're looking to start developing add-ons and whatnot, then by all means you could probably start working on them in the 5.7 beta, just anticipate that some changes may happen that may or may not break what you've written.