I can't speak for the Boyue and Onyx, but I've been using a rooted Nook ST, and it's fast, stable and super feature rich. It also cost me $50
What I want is a larger screen (8" minimum) that will work as a secondary computer monitor. The Onyx is available, but I've read that the A2 refresh mode is poor, and anyway I won't risk ordering from Europe and having to send it back if it doesn't work. I've given up on getting an e-ink monitor for now. In a year or two, hopefully.