Eheim is the best auto feeder out there IMO. There are 2 downsides in my opinion... not having an ability to run via outlet, and not being able to secure it to a tank rim.
The later which is seems you had an issue with is somewhat resolved if you use the eheim feeder in conjunction with the eheim feeding station. The feeding station comes with a little piece of velcro that you can use to "secure" the feeder to the feeding station.
While it is not the most stable, it has worked for me in my experience.
If have an apex controller, you can opt to go with the apex feeder. This feeder is very user friendly in terms of program through apex fusion, but I have heard several occasions of these units failing and dumping in entire canisters worth of food at a time.
I have actually also heard of the same story with the eheim units come to think of it with the feeding door opening up wider while in use, but an easy fix to this issue is the use some sort of tape (usually black electric tape) to tape the door into the position you want so it doesn't move "accidentally"
Hope this helps! Feel free to follow me as I am considering starting a blog here about setting up and maintaining a reef aquarium which will go into some detail about equipment and such at some point down the line.