When surfing aliexpress for technical bits and bobs I occasionally see ads for the above eg:
https://www.aliexpress.com/item/1005010595651848.html
Why do baby chooks (Aussie slang) need leg stabilizers fer goodness sake?
Bumblefoot? Maybe.
But they are used to help a chick with deflicted legs for a number of reasons walk to eat and drink.
I was wondering the same thing. From Google search AI overview (edited by me):
For pets and livestock/breeder shows, I guess. Can’t imagine anybody doing this for a layer or a roaster.
You are correct. They are euthed instead.
Here is a story about a splay-legged chick. Trigger warning: It died of other causes anyway. We’ve used pipe cleaners and the issue resolves (or not) in about a week.
It’s so they can’t escape from the cops!
One of the family’s parrots was splay-legged. We didn’t catch it in time and it became a permanent deformity.
As a protected and pampered pet this was not the end for him, but it did impact his life. He learned to fly before he learned to walk (and was, not surprisingly, a very powerful flyer), could not perch normally (we constructed perches just for him), and suffered from arthritis in his old age.
For a chicken in a flock being disabled is a good way to wind up on the bottom of the social order with potentially fatal consequences. For wild birds such a problem would be fatal.
It’s fairly common for horses (and cattle and goats) to be born with legs misshapen so that their hooves don’t meet the ground flat, thus walking on their toes. This is typically contracted tendons from their legs being folded up inside their mother. In most cases, this will correct itself in the first 24-48 hours after birth, with massage, warm compresses, and just walking around.
But most breeders have devices like splints, bandages, etc. that they and their veterinarian use when more help is needed. But these are often homemade rather than commercial products, because these species aren’t bred in the volume of chickens. But they serve a similar purpose.
So free range chickens can’t get very far? 
On that same page - Anti-pecking device.
Sold by 100 pcs.!
I was so certain this was going to be about culinary drumstick roasting/grilling gadgets. They sure do stabilize the chicken legs.
Because they are getting ever closer to the farmers’ ultimate goal, and that is to have a big, fleshy chicken that sits in one spot and eats but also has ample wings and legs.
Haven’t you ever noticed that every bird we domesticate for farming is heavy and can’t fly? LOL
I’m not sure if this is related, but it might be. And it’s interesting, as well.
Chicken can develop rickets from vitamin D deficiency, just like people (vitamin D helps with metabolizing calcium, needed for strong legs). The stabilizers might help keep their legs straight while they develop.
Now the interesting part – People can use several of the different forms of vitamin D to help grow strong bones, mostly D2 and D3. D3 is cholecalciferol, from animal sources, while D2 is ergocalcifeol, which derives from plant sources, virtually all fungus. It results from ergosterol being exposed to ultraviolet light. They used to make most commercial vitamin D2 by exposing yeast to UV light. A company I worked at made intense flash UV sources that could boost the D2 content in mushrooms by a thousand per cent in under a second.
But the weird thing is that they learned about the difference between D2 and D3 because chickens can’t use D2 to grow bones - they need animal-based vitamin D3. Give chickens vitamin D2 without D3 and they’ll still get rickets.
Can humans use D2?
'Cuz I’ve sure never heard of, or seen, a D2 supplement. … that I recall.
It’s available.
It pops right up if you do a search
As does D3
I suspect a lot of vitamin D supplements contain both, but isn’t separately labeled because little of it is sold directly to chickens.
I’m not sure where one would keep their wallet.
In their mobile phone; just like everyone else. 