Studies have shown that hay nets and hay feeders reduce hay waste by up to 57% compared to feeding directly on the ground.
Hay nets specifically can also limit how much your horse can eat once, extending meal times which helps replicate natural grazing. Remember, horses are grazing animals are 'designed' to graze all day. Using a hay net helps replicate this for domesticated animals.
This study from the University of Minnesota, USA, has a comprehensive breakdown of the styles of horse feeders that work best. The most cost effective option was a hay net, that also saved 94% of hay!
Here are three hay ring/net companies I recommend: