I got the Eheim 3581 based on recommendations and it works flawlessly for the 5 or 6 times I have actually used it. look at the video (not mine). how far you open the sliding door determines how much food is fed and it will do one 360 turn or two for double portions.
I mounted mine on the rim of my tank with velcro. you may have to get creative if you are rimless or dont have anything to set it on.
I only need it for when I'm out of town for extended periods, maybe a couple of times a year so I won't be using it all the time. Just as long as it can last a couple of weeks before needing to be cleaned/dried out... Thanks!