Slow Feeders - Paddock Paradise Wiki
Several options, from homemade to storebought, for small and roundbales
You're the one who has to decide what works best.
I wouldn't bother with the roundbale nets, since you already have squares and would instead get several small nets, and provide a days worth of hay for them like that, hang them on fenceposts, spread out, so they move around. Not much difference filling them with square or round baled hay. The plus side is, rounds can have bad spots, and by giving it in small nets you can see the bad stuff and discard if needed.
I feed rationed hay with small nets. I got me a little fishing scale and weigh the filled nets.