Dwell time is the whole currency
A poster gets one second. A screen in a salon gets the entire processing time. Salons interest advertisers not because more people come — but because the people who come stay.
The eyes are on the mirror anyway. A screen behind the chair is in frame the whole time; one by the entrance only during the wait. Where it hangs matters more than how big it is.
Sound stays off. Your playlist stays your playlist, and nothing drowns out the conversation at the chair.
That long sitting time has a flip side: someone seated for a long stretch sees the same ad more than once. That is why ad share is a dial you turn, not a setting we impose — less ad time means more of your own content and a lower share.