I don't recall ever feeling like an LCD is causing more eyestrain than my eInk devices, as long as the brightness levels are roughly matching the ambient light. Too bright or too dim for the conditions and yes I've felt it.
Ease of reading on the eyes wasn't why I bought an eInk though, it's ability to read at all outside :P Reading an LCD outside IS a huge strain on my eyes, or rather, was the few times I attempted it
