The unit itself is well constructed, and the fit is great, so installation was no problem.
The LCD panel itself... doesn't look great, I think. I was not able to get a good viewing angle at any normal viewing distance, where black didn't start to look blue or purple, a bit brighter than the darkest details. Gives it an odd look that's unappealing.
Contrast isn't too good, and it's a bit underwhelming, even compared to an old DS Lite.
The thing that makes this unit viscerally offensive is that there's visible screen tearing. It appears that the unit uses a framebuffer, but doesn't double buffer nor run at a framerate based on the GBC's original framerate, so every so often an ugly tear rolls upwards on the screen.

I imagine I can't return this thing, but I've already removed it from my GBC. I'm pretty disappointed in what I got.
See the tear in action for yourself in this tiny video: https://www.youtube.com/watch?v=im4nyDud2fM