Following for updates, never heard of anything like this - surely human body heat will be too cold for this to work - not to mention shaking the egg about walking and such, i guess its a different movement type than turning and can be more stressful?
I use a plate, find its best to have it low enough so they can touch the top, but have one end higher so they can move about and find the right temp for themselves, especially as they grow and some might be a tad bigger than others.
Here is a good article about feeding a good diet: https://www.backyardchickens.com/articles/a-balanced-diet-for-your-flock.74212/
I am new to this, but from what I understand they need at least 14% protein daily, so perhaps try supplementing their diet with extra protein?
Are they free range? do they have access to bugs and such? I don't know much about treating issues yet, but it could be that they might not be getting enough protein?
We now have wing feathers starting to come through!
Babies are getting very inquisitive, they keep jumping up on their Ecoglow bed and jumping off!
The little fully black one seems to have a lump on their shoulder, i think it might be from playing too rough. Will keep an eye on it, eating...