The issue is that they are lost/removed/torn. I still like the tags because it's convenient but anyone that wants to steal an instrument can just rip it off. We write the school name with a paint marker on the case but keep the serial numbers on the luggage tags.
I think we replaced 10 of them at the end of this year. I know my road guy loves the tags. Serial number easy to read. Also helps them identify the school the instrument is from quite easily.