opinions on Purina Amplify? Does it work? Is it okay for picky eaters? 

I love Amplify - actually its the only "grain" my horses get

i feed 1lb amplify with their supplments  - their breakfast and dinner is flakes of alfafa 

it 30% fat - my horses love it - even my dogs go in the stall looking for scraps - so doggy approved lol 

My super picky eater had issues with it, but I added it super slow and didn't have any issues. She's so picky she won't eat her grain if I bute someone else and use the same coffee can.

I didn't notice any difference. I fed it for 3 months.

I had really good luck with it on my moms older gelding who was a hard keeper. I could cut back on the volume of grain I was feeding him by adding that in. The very picky mare I had ate it too with no problem. I like feeding even just a little of it to my easy keepers because it just gives them a whole extra level of that fat shine to their coat. 

We feed Omaleen 300 to our foals when we wean them. It has Amplify & Outlast in it. We love it the foals don't back up a bit when they are weaned & stay healthy. We had a old stud horse that wasn't doing well at all. We thought we were going to have to put him down. He just wouldn't hold weight at all. We put him on Omaleen 300 ( We had tried every kind of senior feed, additives, chopped alfalfa,  everything we could think of ) he did great on the Omaleen with Amplify. We were amazed at how fast he improved & we got to spend 3 more years with him.   

I fed it to my horse for a month and a half, trying to get some weight back on her. Didn't do a thing.

Did alfalfa pellets instead. She put the weight back on.

I suppose it is going to vary on the horse.

It is essentially a fat supplement with some vitamins and minerals added and a bit of protein in there. It is by no means a bad product, but if you are just looking to add some weight and/or shine and are already meeting your horse's vitamin and mineral needs, adding some ground flax or canola oil would get the job done just as well.