I've also been using the 1000nits build on my Minix since last fall and it's been pretty solid on most everything I throw at it. I tried CoreElec a few times, but I had problems with it interfering with my Flirc inputs, and some videos didn't run well. I may switch over and try it again as it's been awhile.
Hey, I feel you on the Minix U9-H, but I've been using the 18.104.22.168 1000nits build for about 5 months now without any issue. I tried to make the jump to CoreElec last week but ran into a lot of problems, namely crashes and weird graphical bugs. I'm wondering if other people had issues with this device on CoreElec as well, but as far as stability goes, LE has been very satisfactory, with thanks to wrxtasy. Based on this I'll probably stay put for another couple months if there's no further LE development and I'll give CE a try again.