Hey guys, good news, firemen didn't had to react.
I've installed successfully on my phone (latest FW v15), only had trouble with masking my phone, somehow it didn't change the parameters in "about phone" and and only after few tries managed to start. But, anyway, isntalation went smooth. I've previously hard reseted my phone, and did hard reset after upgrade. It's necessary after, few apps didn't wanted to start.
But after that, it works smooth. Pain is with Store beta app, it updates app veeery slowly, but it's better after it updates itself.
Overall, this build is much better than previous. It's pretty smooth, and didn't had any reboots or major lags. Switching from app to app is much, much, much better then in 8.1, so much faster. I've had a lot of resuming screens with Messenger and it was frustrating, often waiting up to 10 sec and often crashing the app. Now, switching back to app takes only 2 second max, no resuming at all. Maybe even faster. And it stays in memory whole morning.
There is sometimes lag after unlocking and when coming back to start screen. I've had to manually set the apn. Overall it's pretty good. If it doesn't suck up the batter (which I think it will) I won't be coming back to 8.1. Looks stable enough. Almost like Android
Overall, should you try it? I advised on previous build to not install, and won't advise now because of the all the risk which are increased with our phone , but if you wan't to try, can give it a try, it's not unusable as it was the case in past, it's actually good for alpha software.