@M McDindi , we recently returned from SA and utilized 4 AirTags. I went this route based on a good friend’s recommendation. I did wait until the last minute but finally bit the bullet for piece of mind. We flew Chicago - London - JBurg - Port Elizabeth. What I experienced (similar to others comments on here) is that there is a bit of delay in the update. I am guessing it is due to exactly what you mentioned- no Bluetooth device nearby. That being said, I was able to track our checked bag, gun case, ammo case, and my carryon throughout the entire trip. Bring our first trip with guns, I became worried in Chicago when we were literally 15 mins from boarding and the guns and ammo still showed as not having been brought to the plane. I went to the gate counter and explained the situation to the desk clerk, showing them the AirTag locations on the app. They assured me the guns would be on the plane as that is the last thing loaded and the first thing off the plane. Sure enough, right before we boarded, they showed up. I would definitely recommend them for the budget conscious person. I have no experience with the GPS models but would expect they would be even better, just at a higher cost.
BTW- I even used the app to locate my guns in the customs offices throughout the flight. Followed the tags right to the proper location.
I would say either should work just fine.