I use a hay net, not a slowfeeder net, just your average hay net, and I really like it! I bet I would like it even more if it were a slow-feed one! Haha
Before I started using a net, I was placing my mare's hay (about 20lbs, I like to free-choice hay during the winter and she eats about 15lbs/day) on the ground in her stall which worked but she would pick through it, find her favorite parts, then soil the rest. A LOT of hay was being wasted. Since I got the hay net, she still wastes a bit of hay every night but the waste is very minimal.
My least favorite thing about the hay net is that she always ends up leaving her "least favorite" hay in it, in the bottom of the net, so over time, it sort of builds up. I end up using that "least favorite" hay as bedding for my goats so it all works out but I still wish she would eat it all at some point! Haha
And, along with the $$ benefits for me, she LOVES slinging that net around!