I switched over from on the ground to using homemade slowfeeder nets about a year ago and never looked back. I make them out of baling twine and can choose the size of net and openings also, which proved to be great, because I was feeding oat- and 3-way hay until about a month ago.
Consumption, free choice, went from 25 to 15lbs/horse/day. I weighed everything, even raked up and weighed leftovers and spoiled stuff.
I did mix the alfalfa with the grain hay, and had a tub or stallmat under the nets to catch the grain kernels and leaves.
I never had a horse get frustrated, maybe because I started them slow, gave some hay in the ground along with the nets and had " learner" nets with larger holes first.
No pawing at the nets, the eating off the ground happens when they go for the leaves and kernels/seeds.
I got them tied to fenceposts, so I can move them around, to get out of the wind, or sun, or away from the palm tree which throws " things" in the paddock when it's SW wind.
I also noticed my horses prefer eating from the nets, they left what was on the ground and ate from nets first.