I've seen a few people use e-rex's and they seem to be quite sweet, but they are essentially exactly the same as spyders just different cosmetics and name.
E-Rex=Nice. Quite quick, Easy to maintain, not as many plastic parts as the spyder, so far tougher. All in all very good for the price. a nice peice of kit.
-jtl
Hmm, though I agree that they're easy to maintain and good for a starter marker, I would recommend a different barrel than the one supplied; I know that a Spyder barrel would fit and is much longer/more accurate. I used a mate's at the last walk-on I played and had no problems with it until probably the very last couple of games; most likely shoddy paint and a smegged hammer (my fault!!). Overall a good marker, especially for the price you pay!