This is a blast from the past! 
I actually ended up ordering a Savvy Feeder as I had someone locally I could get it from and could see it first. https://savvyfeeder.com/
It worked great when I was at a boarding barn, but I don’t really use it anymore now that I have her at home. I prefer to use hay nets that I then clip into a big stock tank.
But, as for the product itself, it works pretty well. I didn’t realize that you weren’t supposed to stuff the thing chock full so we ended up with a bunch of sharp edges and teeth marks on the grate as she was using her teeth to try to get out the tightly stuffed hay. I spoke the owner and she set me straight, plus told me how to dremel out the sharp edges. It’s really sturdy. My horse would knock it around, turn it over, etc., and it isn’t any worse for the wear.
I stopped using it for two reasons.
First, I feed her by weight, and it’s easier to stuff a hay net and weigh it than it is to weigh loose flakes and then fill the feeder. If you’re feeding free choice hay or by flake, this isn’t a consideration but my mare is a hoover and needs to be on a strict diet.
Second, I think the hay net slows her down more than the Savvy Feeder does (I even tried the grate with the smallest holes). I have a bunch of different nets with different hole sizes that I’ve tried, but what I almost always use is the SmartPak hay bag made out of webbing, with the 1.5 inch holes. If I want to slow her down even more, I use my HayChix 1 inch nets. My set up looks basically like this: https://www.doversaddlery.com/freedom-feeder-full-bale-net/p/X1-270103/?gclid=EAIaIQobChMIseLa3amy9QIVJv_jBx2caQIeEAQYASABEgLPfvD_BwE
Another one to consider that I think looks pretty awesome is the Helix Feeder. https://kiwifeeder.com/ It has a grate with adjustable hole sizes and the whole thing collapses as the hay is eaten down, rather than just the grate lowering.
If I had to choose, I think I’d likely get any of the other three before the Haygain. That one doesn’t seem to have many reviews whereas each of the other three get really good reviews.