no. they often cause more problems then good. how long will you be gone? healthy fish should be fine for a week. i had a tank when i went out of state that didnt get fed for over 10 days. not a single death.
exactly, if it was over 2wks then i'd worry but enstead of a feeder block just pay the kid next door 5 bucks to come by once a week and dump a premeasured amount of food in a film canister into your tank, or get the autofeeders, they're fairly reliable ime.
i agree that your fish will be fine without food for up to 2 weeks. As mg said, i would do a water change before you leave. The timer for the lights is a good idea (since you have plants). Enjoy your trip!