Paying based on tacho time makes a lot of sense since it reflects pretty accurately the biggest expense in running an aircraft: fuel. My club uses tacho time for all aircraft that have a tacho.
For our aircraft without a tacho (DR200-135CDI and DA40-TDI) we use hobbs time and it's a major source of discussion: paying the full price regardless of whether you're sitting at the hold or flying flat-out at 100% towards your destination.