Basically, the boxes, when used with the metal grates, work very well for eliminating waste entirely and slowing down consumption a little bit. If you are really trying to slow down/limit consumption though, the metal grates don't slow them down enough. If that is not a concern, then they work great with one exception. All of the equines did very well with the metal grates with the sole exception of Gabe. Those of you who remember him, may recall that he was a stinking hog about food (sorry Gabe, no offense, but if the shoe fits....). Gabe made his mouth sore because he absolutely would NOT stop trying to bite the grate. If your horses are not stinking hogs about food then you won't have any trouble with using metal grates. I haven't seen any indication that the grates cause tooth or gum problems in the less greedy equine population. If you are dealing with a stinking hog, I suggest using nets instead.
I find that the boxes also work very well combined with any type of hay net. The nets can be secured in the bottom of the box, which keeps the nets out of the mud/snow and keeps the hooves away from the nets. A frame with netting stretched inside can also be made to fit the boxes instead of using the metal grates. I like the boxes because they provide a lot of options. That flexibility is nice when your animal's hay needs vary throughout the year.
The things to take into consideration when making choices between boxes, nets or a combination are determining what your main goals are. If you just want to eliminate waste and make sure the hay ration lasts a little longer, the boxes and grates are a really nice, user friendly, economical and long lasting option.
If you have fatties on a perpetual diet, (like, ahem, mine) I like hay nets with very small holes. One things you'll find is that, over time, the animals become more and more adept at getting food out of the nets/boxes. What slowed them down dramatically at first will lose a lot of effectiveness as they gain proficiency in extracting the food. I have found this to be true with every feeder or net I've tried. My herd has become so proficient with hay nets that I am always trying to think of new ways to slow them down even more. It's especially difficult for me because my crazy schedule makes multiple feedings difficult. I really need to be able to put out many hours worth of food yet still limit intake. Lately, I have taken to doubling up two different types of hay nets. I found that doubling two of the same didn't work for more than a day because they figured out how to line up the holes. Darned donkeys are way too clever for their own good.
If you have fatties on a perpetual diet, (like, ahem, mine) I like hay nets with very small holes. One things you'll find is that, over time, the animals become more and more adept at getting food out of the nets/boxes. What slowed them down dramatically at first will lose a lot of effectiveness as they gain proficiency in extracting the food. I have found this to be true with every feeder or net I've tried. My herd has become so proficient with hay nets that I am always trying to think of new ways to slow them down even more. It's especially difficult for me because my crazy schedule makes multiple feedings difficult. I really need to be able to put out many hours worth of food yet still limit intake. Lately, I have taken to doubling up two different types of hay nets. I found that doubling two of the same didn't work for more than a day because they figured out how to line up the holes. Darned donkeys are way too clever for their own good.
It's hard to tell in this photo, but there is actually a thin, grey net inside of the blue one.
This is the thin net made out of something like hockey netting...
Inside a cheap Chicks net.
This combination will make 6-8 pounds of hay last about three hours. Pretty good considering that they would slurp that down in twenty minutes if fed loose. This combination is also easy to put out on a tree, leave on the ground loose or secure inside a hay box.

I have also been using the track system I developed last year. Their pasture is actually a narrow track that goes around the outside of the field. Although they look to be out in lush pasture, they aren't. Their access to grass is severely limited. Seeing the track get nibbled down to the ground makes my farmer's heart quail a bit, but it has kept the pudge down to acceptable levels while still giving them lots of room to roam. I estimate the track to be about 3000 feet long and they generally go around 10-12 times per day, maybe more at night. Emma is still a bit chubby, but for a donkey living in NY, I don't think she is too terribly fat. I'd like to see her lose a few more pounds, but as long as she does not gain any more, I'll settle for that.
I include Tessa in the "donkey" classification because, so far, she is the one I am having the most trouble keeping weight off of. I consider her to be very high risk for IR and am feeding her the same way I feed the donkeys. I'd love to give her more exercise, but real-world, it's not likely to happen.
Pushing their pasture area so hard, I do worry about them eating toxic plants. While my pastures may look lovely in photos, a close examination will reveal masses of nasty, toxic weeds. Animals are very smart about such things and they won't generally eat toxic plants unless they feel forced to do so. I don't want them to ever feel forced. I also need to be able to leave for work for hours at a time and feel confident that they won't be looking for trouble while I am gone. For those reasons and the fact that they need forage to stay healthy and avoid ulcers, they always have access to some kind of acceptable food. The always have wheat straw in a Cinch Chix net. They get this along with a small amount of hay in a doubled net each day. I like the Cinch Chix nets and would like to get a couple more in different sizes, but they are expensive.
It has taken me a long time to get the straw worked out, but they are doing well with it now. They eat about 15 pounds of wheat straw each day now and their weights have all stabilized. The straw has been tested so I know it has a very low sugar/starch content and the farmer who is growing it does not spray it with any chemicals, which is a real concern with straw. Any straw left in the net for more than a week gets used for bedding.
I would like to increase their exercise and will try to do that by putting their feed out on the track as far away from the barn as possible. I've done this a bit and it does work. However, the bugs have been so bad this year, that I didn't have the heart to keep it up. Tessa does OK, although she hates bugs, but the biting flies go after the donkeys so bad that they come in with blood literally dripping down their legs and their eyes streaming. I've tried sprays and wraps, but the only thing that really works is hiding in the barn away from the bugs. Of course, come winter, it will be howling arctic winds that they'll be hiding from. I am glad to have the variety of nets, boxes, hay and straw that is, so far, keeping them contentedly "grazing" all day while still managing the weight problem.
This combination will make 6-8 pounds of hay last about three hours. Pretty good considering that they would slurp that down in twenty minutes if fed loose. This combination is also easy to put out on a tree, leave on the ground loose or secure inside a hay box.
I include Tessa in the "donkey" classification because, so far, she is the one I am having the most trouble keeping weight off of. I consider her to be very high risk for IR and am feeding her the same way I feed the donkeys. I'd love to give her more exercise, but real-world, it's not likely to happen.
Pushing their pasture area so hard, I do worry about them eating toxic plants. While my pastures may look lovely in photos, a close examination will reveal masses of nasty, toxic weeds. Animals are very smart about such things and they won't generally eat toxic plants unless they feel forced to do so. I don't want them to ever feel forced. I also need to be able to leave for work for hours at a time and feel confident that they won't be looking for trouble while I am gone. For those reasons and the fact that they need forage to stay healthy and avoid ulcers, they always have access to some kind of acceptable food. The always have wheat straw in a Cinch Chix net. They get this along with a small amount of hay in a doubled net each day. I like the Cinch Chix nets and would like to get a couple more in different sizes, but they are expensive.
It has taken me a long time to get the straw worked out, but they are doing well with it now. They eat about 15 pounds of wheat straw each day now and their weights have all stabilized. The straw has been tested so I know it has a very low sugar/starch content and the farmer who is growing it does not spray it with any chemicals, which is a real concern with straw. Any straw left in the net for more than a week gets used for bedding.