While it would probably be fine for the horses, you will hate it when it comes to picking up manure as it will just about the same size. I find with the larger gravel it is hard to get just poop and not a lot of gravel. We are using 5/8" minus for our paddocks
One alternative that's even smaller than the 5/8'' gravel... we recently did some renovations on our place and used crushed granite for some of the high traffic areas and around the barn. It packed in super quickly and is very, very easy to pick. Drains easily and keeps the mud at bay. Doesn't have any pieces that get stuck in hooves as it is sized more like rough beach sand.
I wouldn't use it if you're locking them in the paddock 24x7 because it wouldn't make a good bed - they still would need at least some mats and shavings to have a comfortable place to lay down; but it's been really great for high traffic areas and I wouldn't hesitate putting it into turn out paddocks.
(Ignore the dirt - we scraped off the majority of the old white rock "driveway" and a lot of the old top soil while we did everything else - the grass is slowly growing back!)
Thanks, that’s helpful1. My plan is to put 1/4” minus on top of 3/4” gravel in the high traffic area that tends to stay wet too long. Inside their stalls I do have rubber mats and shavings. Mostly they are free to go in and out, but with our recent weather (it keeps raining!) I have had to keep them in over night a few times. I’ll show pics when I’m finished. Thanks so much for the feedback!