We have used them for years and never seen damage or irritation. I use the tiny micro ones. Color coded for years, introduction time/for sale/not for sale/sold. Different leg sides also worked into our color coding. 10 different colors, primary colors and fluorescent colors.Any concerns about the zip ties rubbing against legs and causing sores?
If our birds get into the neighbouring birds we can ID them.
When someone tries to return a bird wanting a trade or refund, I tell them not to remove the tag before purchase and record bands that leave our property.
But after time in Florida heat, the bands degrade and break off. So we have to monitor bands constantly.
Inexpensive and effect inventory tools.
Never a single health issue.