I have a Yanmar 3GM
connected to a Volvo
hydraulic pump / drive unit because the design of the boat is such that the engine
can't be near the prop shaft.
It works quite well, but its noisy and you lose about 10% of your power in slip which emanates as heat. I had troubles with leaks
and blowing filters but after spending $$$s it all works reliably.
Would I chose it again...I think the answer is no...but maybe modern drives are more efficient.
Vetus have a rather nice looking system in their catalogue.