The couple things I will say about automatic feeders is to use it before you need it, and don't overfeed.
Don't wait until the day you leave to set it up and fill it with fish food.
If you're going to use one when you're away, set it up and let it run several weeks prior to you leaving.
That way you get to see how it works, how the fish take to the food, how much waste is being dumped into the tank and how it may affect your water quality.
I used one with flake foods, and most of the food hit the water surface and got pulled down the overflow before all fish could eat it. I had to make a little floating barrier around where the food came out so that wouldn't happen.
Basically I was feeding my sponge prefilters for 10 days, and the fish got little food.
Poor water quality resulted when I returned from my trip.
They work, but I prefer to have an intelligent friend or neighbor drop in every couple days to feed tanks.
( intelligent meaning one that can follow written or verbal instructions

)