I've used the hay play ball in an outside paddock for ponies on a diet. It does slow them down a bit compared to loose hay (not massively - I think they can get through it quicker than a small hole net) & they soon get the hang of using it. & stomping on it. & picking it up & lobbing it out of the paddock. & kicking it into next door's paddock. Luckily they are robust. You can fit about 3 or 4lbs of hay in it if you stuff it full. Most of the ponies seem to like it & all of them will use it if that is where their dinner is.
I have a hayball for one of mine as she wears shoes so cant have a hay pillow like the others. She seems to like it and it does mean she has to tootle round her stable after it and slows her speed of ewring it down. Also stops her smooshing her hay into her bed 👍
I have one mainly for when he's in earlier during the long winter nights. I like it as it keeps him moving a bit in the stable. Also use it in the winter turnout area, again to keep him moving. Our stables are close to the house and we here him banging it about when we're in bed so don't leave it in all night😁.