It all depends on the quality of the service in your area.
I have this and I have used it with att and cricket. It works amazingly well for gaming online. Though I am in a good service area. If att doesn't work well in your area then this device won't change that.
I'm getting anywhere from 19ms to low 30s ping time and download speeds of over 20 down. While the ping times are higher than a dedicated fiber line, it is still plenty fast for gaming. I have no problems in first person shooters.