As I read in other thread, new ROM.eu Android 7 based has the bootlader locked, it is true for 8.2.1 too? In this case multistep unlock procedure must be applied starting from China Rom developer... very boring.
But I haven't succeeded to flash the TWRP recovery by the way .
I tried twice to do fastboot flash recovery <twrp>.img but despite there was succeeds message at a command line. I found myself with stock recovery.
And by the and I boot to TWRP by fastboot boot twrp.img directly from my PC. And then installed the ROM
I had given a chance to 8.2.1 but the app Gravity screen wasn't working properly. I checked permits and whatsoever but no joy. so I went back to the former stable one. There wasn't any significant upgrade by the way.