When I used them, my pigs would pull all the hay out and use them as hammocks. They don't hold a lot of hay if I'm honest so you'd need to keep refilling them which is no good if you're out during the day. Some pigs may chew them but that's down to the individual.
My piggies have a big pile of hay on the floor. It has multiple purposes; food, toilet, playground, and/or bed. Pigs love it and they eat more of it which is important as most of their diet should be hay. So why not try that ?