I have had a decent experience with the 4GB ROCK64. Armbian provides a reproducible build that I've found to be perfectly stable in practice, and while I have yet to try booting the image, I was able to build the 4.4.x kernel version I'm running, on the device at that.

There's mainline kernel support in 4.14, but I'm unclear as to whether it supports USB3, which, behind the price point and the 4GB of RAM, is the main draw.

I only run the device headless, so I can't speak to the behavior or interactions associated with the graphics engine.