[soulfuldog]

Of course it is, regardless of refresh rate, today's LCD screens being "less tiring", and turning down the brightness when reading on tablets, there is still some artificial light there that will possibly have some effect if you stare at it for a prolonged period.

In normal daylight (i.e. reading indoors without any lights) viewing lots of text for hours on end on e-ink instead of LCD is just more natural for your eyes, therefore more comfortable.

If you only read for say 20 minutes at a time, lying in your bed at night, or if you read with the light shining on your ereader in the dark etc, the difference is probably pretty negligible.