Some people, usually visually impaired, suffer more from eye strain as compared to others.
I have ES6200 40" which came with 2 glasses, most definitely the same as your friends, and have this LED installed in my hostel room, and from a wide variety of viewers, I can tell you that the eye strain (keeping everything constant) varies from person to person, right from feeling nothing (me!
) to a friend who felt extremely nauseous, and he wasn't able to view even for a bit longer!
The price difference is more likely to be due to provision of warranties (local, international, none!). Method of import (smuggling!
) and other various reasons.
By the way, the choice of enjoying a 3D content is very subjective. Some adore it, others can't stand it!
Personally I like it, but it's charm is in viewing only good content in 3D.