I would say those AirTags will be with the iPhones of their respective owners. Mine report as “With you” so perhaps they don’t advertise themselves in this state. The phone will be frequently updating its own location to Find My anyway so no extra power draw.
However if you’re walking by a set of left luggage lockers or through some similar environment where lots of AirTags not with their owner then there would indeed be some overhead. If you work in baggage handling in an airport would probably be telling.
This all depends on the frequency which the AirTag reports itself and the frequency where your iPhone listens out. I suspect the impact would be negligible considering the power draw of the U1 in the AirTag is of order the power draw that the phone must commit.
However if you’re walking by a set of left luggage lockers or through some similar environment where lots of AirTags not with their owner then there would indeed be some overhead. If you work in baggage handling in an airport would probably be telling. This all depends on the frequency which the AirTag reports itself and the frequency where your iPhone listens out. I suspect the impact would be negligible considering the power draw of the U1 in the AirTag is of order the power draw that the phone must commit.