Is one time App purchase good to use for several drones?

Hi, I got 3 drones, Mavic Air, Air 2 and Tello, just wondering if a single purchase of the Litchi app will be good to use on all of them, or I need to make a purchase for every single one of them.

Yes and No.
Litchi is not compatible with the Tello.

but can I use a single purchase for both Air and air 2?

Yes you can use with both DJI drones