I just use hay nets for my blubberous drafty :P I've went from using about a bale and a half to just about 2/3 a bale per day. I started with nets with really big holes, just so she could get used to pulling the hay out, then gradually got smaller holes. Now she has hay in front of her all the time, even if she can only eat a bite at a time. Hay nets are way cheaper than those box, but probably a bit less effective :P
A lot of people also realllly like that those boxes allow the horse to eat with their head down.
I saw someone make a really nice slow feeder. They put the hay in a hay net, then put the net in a muck bucket (the rubbery kind that are flexible) with a whole cut in the bottom middle of it. They put the hay net's tie through the hole in the bottom and tie a big knot so they can't pull the net out. This way they can kick it all around and step on it, but not shake out much hay, and the net slows their eating. My only thought about this method is you've GOT to be sure the net and the bucket have no loops of a size that the horse can get a hoof caught! Make sure the net's got tiny holes and the horses' haven't ripped any larger holes in it.
I've been using my hay net for 3 months now and she hasn't damaged it at all.