Hi all,
I was figuring that a routine update from to16.04 Beta 1 to Beta 2 would be the path for me; not a good assumption, after all, though? 
In other words, would it be better to stay with my perfect (enough) Beta 1 until Stable (rather than upgrade)? 
I just installed Beta 1, Sunday, on one PC which I have been enjoying flawlessly; and I do not have time to re-configure it this week. 
Alpha and Beta stages are development builds designed for testing purposes, not for those desiring a system they can rely on. Changes happen, things break:
… 
Updating via Software Updater normally would bring it up to the latest developments (e.g. Beta 2), so subject to the same risks. These new alpha/beta images serve as a “snapshot” of its development, so clean installs are preferred for those reporting bugs, but not an absolute must.
If you’re not hunting for bugs and just want things to stay exactly as they are, do not update your system for now.
Bare in mind that things will change (but not that much) now until Ubuntu MATE 16.04 is officially stable, it’s mainly fixes. 
Thanks @lah7, as always, for the quick reply! 
I am indeed happy with 16.04 Beta 1; I tried it because of those rollbacks and other issues, you may recall, with my 15.10 install. Subsequent to my 16.04 Beta 1 install, all bugs (at least the ones which might throw me off) from 15.10 were effectively healed (so far so good - perfect, actually).
Keeping with your previous (post-disclaimer) advice, how will I need to pick and choose the rest of the updates - so to just stick with Beta 1, where I am still keeping it current enough though? 
I know you all are mighty proud of your unprecedented work with UMATE-Xenial; it is the talk of the planet! 
The final release comes out the April 21st, so you could wait 30 days without updates. No harm, as you’re not using the betas to actively hunt for bugs and things seem to work fine so far.
Updating anything after tomorrow will bring them up to scratch with Beta 2. They may be flawless, or they may affect things.
There’s no shoving updates down your throat either, unlike some others we know of! 