i don't use the e13, but two of my friends that ride do - they seem to really like them. one of them rides anything the earth throws at him, and he knows an awful lot about bike tech, so if he rides it, i would trust its a good product (he posts occasionally, hopefully he'll post up here).
i use a race face ring myself - its completely smooth, made of metal - i have had no issues with it, but i dont really ride all that hard, and i try to ride without slamming into things a whole lot.
I use the E13 and it holds up really well. I used to use Race Face and MRP bash gaurds, I find the E13 Poly doesn't hang up as much over things. Just make sure you use the washers they provide and dont beast the chainring bolts