I didn't know that HTC uses different panels for the same phone. Lucky for me, all the HTC phones I have used so far (HTC One M7, HTC One Max and now HTC M9+ Supreme Camera edition) are all okay, I do not get eye strain using it at all.
I get eye strain from not just PWM, but also from certain graphics driver implementation, like Intel graphics and some phone's graphics. My current HTC M9+ SC Edition phone is on Lillipop, and I intend to keep it as it is, I do not want to take the chance of upgrading the software in case they made some changes to the graphics driver which might cause eye strain. Even blackberry Z10 can cause eye strain just from upgrading the OS. This is the kind of thing I want to avoid. If it ain't broke, don't fix it.
I have never rooted my phone before, so I am a bit hesitant to do it. Maybe I can experiment to root my old HTC One M7 phone (which I am not using anymore) just to see what kind of panel it is using.