Like tyler, I used Opteka grip for my T1i. After a year the rubber started to peel off and the buttons were harder to press than on the camera body. What's weird is that I bought it with 2 opteka batteries and they were actually higher capacity than canon's one. I've never had any problems with the grip, everything worked fine, but you could see the build quality wasn't top notch. With that said, back in the day the equivalent canon grip was like 300 bucks and each battery was another $50 so getting me the same thing for $40 with Opteka was definitely worth it.
I'd say if you have a cheaper DSLR, get opteka stuff, it works and isn't overpriced. If you have a camera that costs $2500+ then why bother with cheap grips? Just get a brandname nikon or canon, the grip build quality will be the same as your camera and you can rely on it without thinking "omg what if I drop it" Higher-end grips aren't plastic, they're made from metal/magnesium alloy. Some are even weather sealed.