We have an AirTag on our dog. She's a Great Pyrenees and the previous foster thought she would jump fences so she threw one on her. She came with it and I never saw a reason to take it off so it's still on her. One day during a pre-storm she did hop the fence, or something we don't really know how, and got out and the AirTag led us right to her in the bushes at a house 2 miles away from our house.
Couple things I learned about AirTags:
1. They work off the Find My network on your iPhones or other Apple devices. They do not phone home to a server somewhere and update their status at regular intervals. Someone with an Apple device that has the Find My network enabled needs to be close and it will use that device to ping the location.
2. If no Find My network is close, it will not update.
When the dog got out, I was at work and one the phone with my wife telling her where it was reporting she was and sending her screenshots. All of a sudden, she would be 100 yards away. 10 - 20 minutes went by, no change, then again another 100 or so yards away instantly. Finally I joined her in the search and while we were walking in an area that we thought she might have headed towards, I got multiple pings in the same location she was before. We headed back there and sure enough, she was hiding in the bushes.
The issue we had was we would only get pings when someone was close with an iPhone. This could have been someone walking by her location, maybe the people in the house had iPhones so it would ping when they got within distance to connect or whatever. Point is, if nobody was close, no ping and no location update. So if you put one in your luggage and lets say the last time someone with an iPhone was near it was at your departure location, then when you get to wherever you are going and only Androids are around, it's not going to update the location which leads you to the situation that Todd had.
In the end, I would definitely recommend the AirTags. You just have to understand how they work and don't expect them to update constantly. And I would 100000% recommend attaching one to your dog.