Ok, most work ok if you position them away from water movement as they can clog up.
I used one when I went away for 2 weeks and it was fine. I would, however, suggest that if you do buy one set it up as per instructions and watch it for at least a couple of weeks before you go. That way if it does fowl up then you will be there to prevent trouble and to make alternative arrangements.
BTW unless specialized fish they will be perfectly ok for a week to 10 days without feeding at all.