I got a set for our travel bags, not for the plane, but for the bus and/or train travel in Europe. It concerned me that on a Flixbus from Rome to Sorento, I couldn't see what bags were taken out by passengers at intermediate stops. Then, I also thought about when we store our bags by the door when boarding trains - especially crowded ones, and again, you can't always see what people grab when they leave. Granted, I've never missed a bag, but it seemed like a bit of insurance.
The airtag did come in handy when DELTA didn't have our bag in the ATL airport after returning from LHR last fall. Interesting story: We were delayed arriving at the baggage claim area, and one of our checked bags was missing. Delta supervisor had someone go back to the plane to check the baggage area because he said that they just leave bags on the plane. Then he sent me to the missing bag claim area where I was told the bag was in customs. According to them, customs takes bags that are not claimed expeditiously to do a "security recheck". He told me it would be returned the next day. There was no way to verify the story, and I was staying in ATL overnight so I returned the next day. I located my bag on the bottom of a luggage cart, invisible, underneath many bags. The employee helping me was thankful for the locator so he didn't have to move all the bags. I was thankful for it to find my bag! I had never heard of the "customs security recheck" before.