vaz
Hisense A2 pro has android 7 (no frontlight)
Hisense A5 has android 9 (with frontlight)
Hisense A6 has android 8 (with frontlight)
For me, Hisense A2 pro is the phone which has saved my life, as I can use it without any problem. Hisense A5 it gives me eyestrain with or without light, and maybe itˋs worse with light on. I am not sure but I am not going to test again. I would like to buy and test the Hisense A6, but 360€ for a phone maybe I canˋt use itˋs not my idea at the moment
As being rink the only screen I can look at, I am a very experienced user. I use Onyx eReaders since some years and never had a problem with eyestrain, and they have had android, which saved my life. But recently I bought a eink phone with android 9, and this makes me dizzy even with the light turned off, so its possible the problem is with android 9.
My older onyx had android 4 and 4.4, and the one I am using right now have android 6 (8" of screen). I really want to test the newer models with android 9 but I am afraid it can appear dizzynes with that android version.
If Onyx keeps its word of upgrading my actual eReader to android 9 we will have a very valuable information about eyestrain related to android version
So for now, I can say android 4, 6 and 7 (the one in my eink phone) on an eReader are a solution for me
I have installed the latest chromium-based Microsoft Edge browser, it is now available for W7/8.1, I believe it was exclusive to W10 before but I could be wrong.
After a few hours browsing, text seems very legible (maybe they are proprietary M$ fonts), and there seems to be less strain happening than Chrome/Firefox right now. I would recommend giving it a try if you're using Windows.
Edit: Looks like it is available for MacOS and also a soon to be announced Linux version. It is supported on Windows 7 until January 2021.
hpst thanks. That's why i tried onyx as i hoped it will solve the problem of small display in amazon oasis. In fact, all onyx features are perfect except the strain issue. Before i post here, i thought onyx cheated in ink display and maybe sony quality like amazon but seems andoid can be a cause. I would not mind the cost if it has zero eye strain.
Beware the DPT-R1 isn't really meant for reading books...rather notetaking and PDFs. Some of those huge niche devices have bad e-book reading/management experiences due to software not being optimized for that task. They also mostly have horrid battery life. I'd read lots of reviews...especially since that device is something like 6-800 whatever currency.
Older E-Readers were better than new ones as they didn't have all the light diffusing layers and capacitive touch layers. E-Ink Pearl was the clearest I have ever used and was like the letters were printed on the surface, but everything now is Carta and those all have the extra layers which diffuses clarity and needs the light to counter even though they are higher resolution. They can look good in the store or with the light on and fonts right, but are never as clear with lights off. Sadly like most tech they are chasing bling and "features" at the expense of the core experience. It would not surprise me at all if the race for "cool" undermines the comfort of the reflective basis with PWM/dithering/whatever. It's also ridiculous that they charge 200-300 dollars for many models of this single purpose old tech device.
hpst
You might be right about the android as a cause. It's weird because e ink readers are meant to be easy on eyes. I think the ereaders companies will destroy this benefit and will end up on the same led/lcd eye strain cycle. Unfortunately improving ereaders means more eye strain.
I am not marketing amazon in any way but i thank amazon for their real ink reader. The new amazon oasis itself has to be set 0 frontlight to be perfect. I don't understand why amazon don't produce 10 inch ereader. I wanted to switch to 10 inch that's why i tried onyx. If anyone here tried sony ereader? I am hesitating to try because it has android as well.
I found any animations on e-ink screen to make me feel dizzy and nauseous. Something about the grainy, uneven way they refresh I think. I had an older onyx device that never animated and that was fine for me to use, but when I tried an e-ink phone using android animations/scrolling would trigger me.
Onyx devices use Android as their OS right?
It's conceivable that IF dithering is a problem for us, that Android based devices, because it's somehow baked into the OS, have it even if they don't need it. This is 100% speculation. If the light was on we could blame PWM as a possibilty. The Kobo Forma has PWM. Also lights being set to "off" aren't always fully "off". The Kindle Paperwhites (at least older models) would still have the light on very dim even at setting "0". We know Dasung monitors dither.
Since Kindles use their own OS maybe it's dithering, they don't do it, and that's the difference in your case...or maybe your post is Amazon marketing poisoning the well since it's Prime Day 
I also know that even safe devices can seem like they are straining me if I am already triggered, or afraid they will. Sometimes it's hard to tell.
I am currently using amazon oasis without any issue at all even for whole day. But once i switch to onyx boox max i get eyestrain within 5 minutes. I also tried another onyx ereader with backlight turned off but still the same issue. Now i am on amazon oasis. Anyone has the same issue.