I own a Etek3 LT.
GRN - Glass reenforced nylon - probably a lower grade, but the same stuff a glock handgun is said to be made out of.
The three pieces on the marker that are made from the substance are the feed neck, the grip/trigger frame, and the eye covers.
I can't see the eye covers ever being an issue, as they're eye covers. Most shots come at you from a forward facing position. If your marker is 'up', it should hit you in the vertical regulator or hopper, not in your eye covers.
The feed neck, I'm a bit weary about - I want to replace it, but I'm also holding off, waiting for it to break on me. It hasn't yet, and I've taken some pretty epic-fail-worthy dives (kinda surprised they haven't found their way to YouTube yet). Honestly, I'm probably going to be upgrading to the AM frame kit before I get a college try at breaking this thing.
The trigger frame. Yeah, I've felt it bend a bit while tasting astroturf - palms up, of course. The first time it bent, it bothered the heck out of me, as I own an old school tourney marker and I thought I'd just bent a metal grip frame that would be hard to replace. Turns out the LT returned to the shape it was originally. No problems.
Ultimately - Unless you're hardcore about having all-aluminum markers, or are colorblind and have issues seeing certain colors - preventing you from programming the marker, save yourself the cash and spend it on a better loader/mask.