We have a shepherdess, I couldn't be without it now. Each year we raise between 15 and 18 tame lambs, they go on it for 5 - 5 1/2 weeks. Growth rates are improved with lambs on the feeder and can wean slightly earlier. We have 7 on it at the moment and they've had 7 litres of milk (full bucket) twice a day.
We put ours on as soon as they come to us at a couple of days old, obviously for first few days I put them on the feeder every few hours but within a couple of days they get the idea.
Think we've raised around 45 lambs in 3 years on our feeder and only 1 has never taken to it and had to remain on the bottle. Huge time saver and much more natural, I don't like leaving young lambs overnight without milk and this is the biggest advantage for me.