I have tried the last 3 previews on my fab 1320. It takes some installing, you need ages. The gears spin for so long you get hypnotised! When successful, it does look good, with nice features added. That latest one (581??), also works well, BUT, on my 1320, the start screen locks / freezes, leaving the store, start screen locks. Lots of resuming, Cortana slow to read texts, she doesn't update, the circle doesn't grow / shrink. The size of the time on glance is so big Stevie Wonder could see it. Several restarts required when the start screen locks, although, you can use Bluetooth to text and call. Weird or what??
It is getting there, but we need the firmware specific RTM for us.