I have always heard a lot of negative things about using hay nets. People complain about almost everything about them. They are hard to fill, a pain to hang and on and on and on. I use the slow feed hay nets ($8 slow feed nets) and love, Love, LOVE them. My horses can have hay in front of them 24/7 and something to pick at to keep them full, occupied and satisfy their grazing needs.
I agree that filling them can be a royal pain in the ass, unless you have help. Someone back in the days on the FHotD blog had mentioned using a laundy basket. I found a Lamper at Target for $10 not long after moving to Houston.
Simply drape the net over the Lamper like a garbage bag. This will hold bout 3 flakes of hay. which will last my guys sometimes for 2 days.
If you pull it over the sides where the bottom of the net is about half way down, as you drop the hay in it will pretty much fill itself as the weight of the hay will push the net to the bottom and pull the sides up. Then just pull the string to close it and also to get the net out of the "lamper". You have a full net in a matter of about 30 seconds or less. Hahaha
Another thing I use is snaps on my nets. I like this kind of snap because there is nothing for the horse to grab to help them undo it. They are also relatively cheap and they last. No more trying to tie the nets up, tying them up and having the horses pull them loose or any of that crap. It's also much quicker to hang them and also take them down to fill.
Wrap the string over something high enough to keep the net up where it belongs and put about 3 or 4 sections of string thru the snap. Done! Keeping the net up where the horse can't paw at it, reduces the chance of them getting a hoof or shoe caught in it. This also keeps the hay from getting wet or dusty from being on the ground. This also works in the trailer for hauling.
One of the girls at the barn that feeds for me had recently bought new nets. Since they don't come with snaps she told me the other night that now that she has to tie them, it's a total pain in the ass! She was going to buy snaps in the morning....