As the owner of three aircraft that are leased to a flying club I find the idea of putting a PLB in each aircraft a recipe for trouble, the chances of the PLB staying in the aircraft long term are minimal and eventually someone will accidentally put it in their flight bag and the aircraft will be grounded untill it is found or a new PLB sourced.
The only real option for the commercial operator is to fit an ELT to the aircraft and make sure it is fitted some place that those renting the aircraft can't get at.
My guess is that in the long term a permanent ELT will be cheaper than replacing the PLB's that go will missing in the flying club environment.