I've used several battery powered ones over the years and they all work fine. The issue I have with them is they feed 12 hrs apart. You have to time it right so the lights are still on when the food drops both times.
I've used the Rondomatic. I would never buy one again. Too expensive, unreliable, hard to load, and it crapped out after a year or so. I tried to take it apart to fix it which was completely futile of course.
I should point out that I was using it for daily duty, not vacations. It took me 10 minutes each time I had to refill it weekly, which became a serious PITA. They could easily redesign the drum part on top and make it 100 times more user friendly.
Thanks for the information everyone. I'll probably go with one of the Eheim feeders. They seem to be popular with a lot of people. There's a twin model out now that looks interesting.