we have these at our new yeard and we was all worried that they wouldnt understand what to do with them but they all just seem to have worked them out, and it didnt take them long at all, a few were a bit weary about the noise when they were re-filling but they are all happy now!! An they are sooooo much easier
When I moved yards my mare was terrified of the auto water drinkers, she was fine initially until they sounded like a large snake when refilling and eventually I had to give her a bucket as she was parched in the morning, her son had a more sensible approach and just learnt it wasn't going to eat him.
They usually figure it out for themselves fairly quickly. I've only come across one that would'nt use them under any circumstances - my old girl Royale - I had to fill buckets for her.
It can help if you hold horse by it and splash the water out so it fills up with your hand in the bowl and they get used to the noise with 'Mum' there to save them and if you've splashed them too so much the better!
They soon learn, even my foals learn well before they are weaned.