I've installed the 4.0 Alpha as well and have been running it a couple of hours now. So far everything seems to be working great - dragging application windows to the DisplayLink screen and moving them around is very smooth. Maybe not quite on par with my Thunderbolt 2 connected displays but very close
One thing I noticed was that the macOS menubar renders correctly now - no more faulty transparency and greyed out menu items are also readable now. I assume it has to do with the Metal optimizations.
All in all I'm very satisfied - great work guys! 👍🏻