There is also a Eheim Everyday Automatic Fish Feeder that is basically the exact same thing, you can find the fish version cheaper on ebay. It attaches to your aquarium rim via plastic thumb screw or you can just rest it on top of the canopy.
The operation of the unit is pretty simple, fill the container full of pellet food, adjust the opening of the little door so that it drops the desired amount of food, and set the feeding time. The translucent box rotates so food falls from the opening. You can set it to do one rotation of multiple rotations and multiple feeding times. There is also a button you can press to manually feed.
Pros:
* Simple setup and operation, very configurable
* Included batteries lasting over a year now on 1 feeding a day
* Has a fan to help food stay dry and fresh
Cons:
* I find it works better with round pellet food or food that has a consistant size
* Not super accurate, doesn't deliver the exact same amount of food every time