I have the Eheim twin feeder, it works, but I find it massively overfeeds. I guess it depends on your tank size, number of fish and how much food you want to go in. I had small sinking catfish pellets in one side of the feeder and flake in the other to begin with. Testing demonstrated that although I wanted about 8-10 pellets in the tank for my Corys, it would feed 40-50 on the lowest possible setting! What I eventually did was empty all the food, then make up a mixture of bulkier flake with the catfish pellets mixed in to it and put that in one side of the feeder. The other side I left empty and set not to run. I then had it dispense one turn once per day and it was hit and miss with what it delivered, but with the mixture I was getting less pellets.
The results were that my fish were fed, but it definitely still overfed. My skimmer was totally gunged up with rotten food after 8 days away and the tank looked way dirtier than it ever would when I hand feed. I did an 80% water change and cleaned everything up and had no knock on issues, but it was not ideal. I would still use it again when I am away for long periods, but advise caution. I would also advise the cheaper single Eheim feeder and make up a mix unless you really need to be feeding different foods at different times of the day.
