At the same time, we put out one of our Grandpas Feeders, the idea being that we want them to get used to it right from the get-go rather than having to move them over to it later. After one day, we removed the other feeder so the only feeder they have (when not in the shed) is this one.
Because it is in the locked-open position, they have no trouble using it. Here they are aged 4 and a half weeks.
EDITED TO ADD: The newer Grandpas Feeders have a grill. This is designed to prevent birds flicking the feed out, but would also have the added advantage of preventing the chicks from getting in to the feeder.