optix Thanks for that idea, yes a used one is the safest approach.
Usable Smartphones?
optix amazing. If the e ink screen can really handle all the apps with that refresh rate then it is definitely worth it. Thank you for posting. Will find out the price...
It doesn't use backlight, more info at https://en.wikipedia.org/wiki/E_Ink
Fyi
Feel free to create a new thread for each smartphone 
Just tag it with Hardware / Phone + Usable
optix I haven't found any reviews of the Moto X 2014 testing for PWM, or any camera tests on it. From your experience would you say it is PWM free, similar to galaxy s2?
I can't guarantee you that it 100% doesn't flicker at any brightness level, as I've used the phone one time for just a little more than 1 hour. During that time it didn't cause me problems and I had the brightness turned up to max. It would be the best if you could test it yourself =)
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My HTC One M8 was the best phone I used since the Galaxy S2, and was 1000x better than my Xperia ZL (which I suspect used PWM). It still wasn't good enough to use for more than 30+ seconds though. I bought an iPhone 6S and although it causes eyestrain and headaches more quickly, I can get far more done in less time. Since I am not doing any colour-sensitive work and don't care at all about how it looks, I inverted the colours. Otherwise I find the iOS7+ theme far too harsh on the eyes, which amplifies whatever hardware or driver problem there is.
Using these settings to reduce eyestrain:
Min brightness
Zoomed
Inverted colours (must change wallpaper to pure white so it becomes black)
Night Shift (scheduled to always on) (doesn't work while colours are inverted)
Grayscale (at night)
Reduce motion
Reduce transparency
Reduce white point
Increase font size
Bold text
Using voice commands as much as possible
Of course none of these reduces the underlying problem. they just delay the onset and allow me to get in and out before a problem starts.
Still the screen seems offensive. I think it is the lensing effect (to increase readability in the daylight) as described on the Apple support thread.
5 days later
Hi, about LG G2 - it's first phone which I can use since my iPhone 4 but only with bluelight filter from play store turned on 25-30% without this screen is blueish and got pain after few minutes. So I hope using other LG like 4, 5 or V10 with this filter should be ok for me. When trying those in store it seems to be ok.
I have iPhone 6 and it's usable only for 1 minute with min. brightness I feel eye pain after using this. Had Macbook Retina 2015 and I gave it to my wife and using now her old Air with min brightness for few hours it's usable.
Ok, so a quick update.
My HTC One M8 (my primary device at this time) has the following screen:
m8_lg_novatek_panel
PANEL_ID_M8_LG_NT35695
Since upgrading the firmware to the Marshmallow-ready firmware, it bothers my eyes more than before. Everything is a little harder to look at. I will be downgrading to the Lollipop firmware shortly, looks like something specific to Marshmallow is making the display drivers unusable for me.
I've personally narrowed my problem to a combination of Blue light and FRC/Temporal dithering. PWM doesn't seem to bother me very much at all. I've discovered that some devices I have used for years without issue have DRASTIC levels of PWM. So that really isn't the issue.
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Amendment to my earlier post: I can only use my iPhone 6s for a few seconds now. The dithering is very obvious, but I don't know if that's why it hurts. A very costly mistake for me.
3 months later
I'm typing this on a OnePlus 3. Been using it for 3 hours straight. It's an "Optic AMOLED" screen with dual polarizers. It uses PWM at least at lower brightness which I confirmed with my iPad camera. Actually I'm in the PWM zone almost the whole time. A little eye strain, probably because I didn't use auto brightness at first. I wanted to stay out of the PWM range which notebookcheck already tested to be at 0-10 %. But it is definitely larger than that. Knowing that the OnePlux X was said to be at 25 %, I selected around 30-40 %, which was probably too bright indoors. Now I'm using a manually adjusted auto brightness. It feels much better than those devices which I had to turn off after just a few minutes (even seconds). The next few days will tell if this device is a keeper. I will report back.
JTL They did a small early test in German language: http://www.notebookcheck.com/Test-OnePlus-3-Smartphone-Erster-Eindruck.167713.0.html
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JTL I'm having doubts that notebookcheck is reliable. Or maybe xiaomi has different versions of the same phone.
Using their recommendation for no pwm i bought a xiaomi redmi 3, and it gives me terrible headache. Since you cannot return phones here, i'm trying to see if i can use it at 100% brightness + f.lux like mode.
BTW, you talked before about LG Nexus 5. have you tested it yourself in prolonged use ? did it cause any trouble ?