Strictly speaking, the PLB is not mandatory, it is actually a concession so you don't have to install a fixed locator beacon in the aircraft. You must have 406 MHz transmission and 121.5 whichever you use.
Microlights, homebuilts, gliders and balloons are exempt the requirement.
The full text is here
https://www.sia.aviation-civile.gouv...2008_10_FR.pdf
You have to register the PLB with your national authority, and you can use one for as many aircraft as you like. (obviously one at a time) It is not required if you don't leave the aerodrome circuit
