The problem with PWM is that you really can't see it. It is only measurable with special equipment.
Moreover, it's a very technical detail. I don't think the average customer is even aware of its existence.
Nevertheless, in susceptible people and depending on how it is implemented, it can cause eye-strain and headaches. This is definitely something that shouldn't be discarded as "can't see it, doesn't exist". Notebookcheck for example checks for PWM on every display they test. This is a huge topic.
Some people say that the Kobo Forma uses PWM. There's even a poll on this forum with 6 out of 51 participants saying that it causes eye-strain for them:
https://www.mobileread.com/forums/po...ts&pollid=2051
I don't think the numbers are reliable. But it's something to keep in mind. Regarding the libra h2o, you're right, I couldn't find any complaints. But the device is barely out yet. I wonder what will turn up in time.
To clarify this, I used the chat option on the kobo website. They told me they would forward my question to the technical team and get back to me. Well, let's see ...