I've been using my Illumina XL HD for one month now, and all things considered, I'm very happy with it.
The form factor, screen quality, choice of OS, battery life, and overall product design are perfect both for reading manga and technical books and for browsing the web.
The only real issue I'm having is that
taps quite often don't go through, so I have to try tapping again 2 or 3 times to turn the page or click a link. My unit came with V1.0.0-2017112317 which I guess is the latest version. I'll try emailing support about this problem.
Other minor issues, in no particular order: no SD card slot, you have 13 GB for your apps and data and that's it; no hardware "volume" buttons to turn the page with, which compounds the tapping issue; the built-in screen locker is somewhat slow / broken (when turning the device on you can use it for several seconds before the screen is locked!) and one time I found the unit locked with a different screen locker (maybe the stock OS one?) that didn't recognize my code, so I had to reboot; the front light is very cold (blue) which is not the best when reading at night; everything feels veeeeery slow compared to a regular Android tablet or phone, even cheap ones.
Don't get me wrong, AFAIK this is the only reader being sold right now with a 8" HD eInk screen and Android OS, and it does a pretty good job. I'm very happy with it! The OS alone is a huge improvement over my old PocketBook InkPad.
The apps I'm using the most, apart from the built-in book reader, are Firefox with uBlock Origin extension and
Tachiyomi, hands down the best app for reading manga (make sure you disable page transitions in the settings.)