I bought four AirTags and have been using them for a few months now. One of them is in the car. That’s the one that gets used the most, and I specifically use it to easily find my parked car again. Alex can now track it with his phone as well, which is handy, and it works well and simply.
Another one is in my suitcase. On our trip to Lanzarote, I used it to check whether the suitcase had arrived in the same place as we had. Everything went smoothly, so it was reassuring to know, though not really a surprise. For the other two, I haven’t yet found a truly useful purpose.