All my fixed-wing machines utilise an airspeed switch, which operates at 40 kts, enabled by the engine oil pressure switch. This ensures that all maintenance activities are related to flight time, and not hanging around on the ramp. There is also another system availalble with an integral tach wired into the gear warning system.
Obviously if you're trying to make money from your aircraft, the more you can charge for sitting at the ramp, the better. We are in the opposite situation, just wishing to base our maintenance operations around actual flight time.
We do not use a Hobbs meter, instead wiring the system directly into an Astrotech digital clock.
All our helicopters utilize a similar system, utilizing an engine oil pressure switch, coupled with squat switches or collective position switches.
Simple, Reliable, accurate.