Our group aircraft had both hobbs and tacho. The tacho was only available on one of the pages of the menu so hobbs was used for simplicity in charging ourselves. Tach was used in the engine log for checks etc.
The hobbs. which was master switch and oil pressure activated recorded 16% more.
The flying club I was a member of some time ago used takeoff to touchdown plus 10 minute which was very fair but was occasionally abused by the hirers.
D.O.