I have three Busy Snacker slow-feed hay bags, and I love them! I understand concerns about flexible hay 'bags', but have no concerns about the Busy Snackers!
However, the downside is, they are not going to hold up much more than a year or so; the flat nylon is fraying severely in the area where the horses 'work at' the most while eating. I routinely 'burn' the frayed edges, which had helped(nylon will 'melt', sort of 'sealing' the frayed edges), but still, they are gradually 'wearing away' and will eventually break down.EDITED TO CLARIFY: It really is ONLY the one Busy Snacker that I use for my larger, more aggressive eater, B-sized gelding, that is fraying/frazzling on the bottom 6" or so. He really 'gets into' eating his hay, and while not seeming frustrated, he is very assertive in pulling the hay from the net. The other two nets, one of which I am not even using at this time, and the other, which is in twice-daily use for a 30" mare, so is never filled as full, have held up much better, and 'should' last a good bit longer.
Even so, because of this factor, I am working on making 'slow feeders' out of my 'regular' feeders! I began with my 8' long metal feeder, which is the only one which serves multiple horses(just 2 now.) It has a V-shaped hay rack above 'troughs' below, a standard design. For each side of the V, I cut two rectangles of 2" X 4" lightweight welded wire, as long as the length of the feeder. One piece was ONE 4" space shorter than the other. Then I laid each shorter piece on top of a longer piece, offsetting it so that 2"X 2" openings were produced. I used a very fine galv. wire to tie the two layers together at intervals. Laid each 'set' of layers on one side of the V,making sure the wire 'ties' were pointed toward the INSIDE of the V, so noses wouldn't be scratched, then used small cable ties to fasten them to the 'bars' of the V, again making sure the projecting ends were pointed INWARD. This made a very efficient 'slow feeder'! The cable ties occasionally break, but are easily replaced.
I am currently working on using the same priciple to turn my 'hang on the fence' plastic barrel feeders into slow feeders. Mine are made from 30 gal. plastic barrels: I created them myself, about 18-20 years ago, and they have held up very well; now I hope to make them even more useful! It is proving a bit more of a challenge to 'fit' two overlapping layers of the 2" x 4" wire into the hay rack section of the feeders, as the hay rack 'tapers down' in shape, but I am taking my time to get it right! Hopefully, the feeders done this way will last and last, and I can save the Busy Snackers for use when traveling, etc...as I really don't want to have to buy replacements every year or so.
Margo