I think there is a market... as many backyard keepers deal with aggressive hens as well. Lot's of people keeping stag pens these days to.
My friend told me about this a couple years ago... or at least I thought so, and have recommended it a few times already! I thought it was a great idea. I can see it being fairly effective for SOME birds.
Turns out she meant they just added a zip tie to the leg to make the chicken look "different" than the others.. and said it worked for THEM to take that bird down a notch or two.
The question asked about unrestricted breeding is a GREAT one!
I think I would be comfortable pay $10 for a well made quality product that is an alternative to kenneling or putting on a tie out. Meaning leather ankle holders. Maybe $7 for one made from thinner Nylon... as seen on game cock tie outs.
Heck, you could even add a weight to the hobble if needed. Slow 'em down a bit more!
I mean I won't personally keep an aggressive rooster (or hen).

I do what it takes to maintain my flock and it's long term genetics. But there are a lot of people who do keep unruly flock members around. Part of the issue... put out a good product.. everyone wants to DIY it to save 50 cents.
Good idea, I'd love to see your design.