These cheap galvos are an interesting quality. I bought some similar to this and the casings and mounts are great but the electronics and feedback leave a lot to be desired. Unlike the peachy homebuilt galvos which are open loop these are closed loop and rely on a PID controller and reasonable feedback. Unfortunately the feedback in the galvos that I received are optical, there are two light sensors, an LED and a piece of glued cardboard on the spindle, the position is apparently sensed by comparison of the two optical sensors and the cardboard baffle moves and changes the proportion. I can't believe that the accuracy of these is actually any better than the stock peachy galvos (although they will be faster but they do burn significant power).
Also if anyone out there does purchase any of these to play with then I strongly urge you to use your own power supply. The questionable quality of the PSU I've received vs the energy you can get from mains is just not worth the risk.