They work great but you have to remove the speaker from the Air Tag because it "beep beep beeps" very loudly and NOTIFIES the "theif" there is a tag nearby and points him or her right to it IF s/he has an iPhone. That is to protect PEOPLE from being tracked by strangers. Even in a case it can be clearly heard. Speaker removal is not too difficult but a "smart thief" can easily discover it. So with or without speaker it can be found by a "smart thief" but with speaker removed it's harder. Apple has recently increased the volume of the speaker in a recent firmware update to the Air Tag for protection. eBay and Etsy have removed all sales of "silent" Air Tags.
Here's a video to do it:
https://www.youtube.com/watch?v=8vAQNedIa0o