I have had these bands on my birds for less than 3 months and the numbers have rubbed off! I now have a bunch of birds with pretty bracelets but can't identify them! The bands are sturdy and won't come off unless cut, so they are durable. They are also fairly inexpensive and you don't have to fuss around with sizing the birds' leg.
If the numbering process could be more durable, I would likely buy again.