AirTags aren’t meant to get stolen items back. That just isn’t the use case. How does this compare to actual GPS trackers like https://monimoto.com/?
That device you link to is more expensive but would never alert the person being stalked, so I suppose that might justify the price.
It's about 10x the size and 4-5x the price.
Probably worth it for a vehicle, but maybe not for a backpack.