First impression is good. Here's some thoughts:
1. I had an uninstall bug in 12.3.3154 that left behind a hidden directory, which was a bugger to remove -- Had to boot to DOS and use DELTREE (ticket submitted with details). I've tried an install and uninstall of this beta, and it works fine.
2. The GUI seems to big and can't be re-sized in typical Windows fashion.
3. Colors aren't much of a concern to me, but maybe it would look more business like without the purple accents, just stick with Orange?
4. The notification "bell" in the upper right corner stays red even after dismissing the notifications, but it went away after a reboot.
4. After a Smart Scan the GUI shows the performance issues details with a sideways wipe. The horizontal arrow in the upper right corner is confusing -- Suggest using the traditional [X] to close.
5. The separate window for settings seems a bit awkward. By opening "subscription information" from the tray icon, then opening the main Avast interface, then clicking on settings in the lower left -- I had 3 windows open and could not go to the main GUI without closing the last settings window, but could get to the first settings window opened via the tray icon. This is not a big deal, but it seems like it would be better with a single window with tabs/menus of "status", "protection", "performance", "settings" across the top.
6. Clicking on the ? of the main GUI brings up the help window, but the help window's menu disappears before one can click on any of the choices.
No crashes or weird behavior noticed, but I'll keep trying...