I use a
Fishmate auto-feeder which I've had for 10+ years, following my ravenous goldfish (RIP) ferociously attacking and completely consuming a slow-releasing food block in the space of 45mins, and following being let down by humans on too many occasions (who changed their minds about being able to turn up) or who neurotically thought that the fish were ill and contacted me when away for my opinion which in turn caused undue anxiety for me.
I had a great tank lid on my old tank, and it sat on the in-built, sturdy condensation tray above the feeder hole, allowing the top lid to remain shut over the top of it; however, on my current tank, I need to keep the lid fully open, place a condensation tray in its place (in which I've cut out a feeder hole), and then set the auto-feeder on top of that. This doesn't feel as secure as with the previous tank.
The auto-feeder itself works well but, over time, has developed a few "issues" eg: once the food is placed in each of the slots, it's necessary to adjust it in such a way that it's on the verge of depositing the first feed otherwise it actually misses out the first feed and only starts when the second feed is due; over the 10+ years I've had it, more moisture/condensation seems to be in the air and affects the food quality by making it soggier (this definitely wasn't a problem in the past and seems to be independent of the auto-feeder itself) - I now need to leave the top cover of the auto-feeder open in order to minimise this.
I used to use goldfish flakes and pellets in the auto-feeder which were larger than tropical fish food, and, over time, only used pellets because of the sogginess issue developing. With the tropical fish, in each feed slot, I now put in a few flakes which I chop a little to make smaller, Hikari micro pellets and Hikari micro wafers. I try and make every slot slightly different eg one or the other of these 3 foods nearer the edge of the slot, just in case a clogging problem does occur. There has been a little clogging on each occasion but not so much that it's stopped the food getting through altogether.
It would be vital to test out any auto-feeder that you buy for a week or so before going away, in order to identify any issues with it, and ensure that you can trust that it's working when you're away.
Hope this helps.