Depends on how it is implemented, and in comparison to what. Also, with a constant speed output shaft, you can have a normal synchronous generator, which utilities are much more comfortable with.

But it all depends on how well each particular drive train design is done. For example, Siemens is convinced there is no better alternative to DD. Vestas says the opposite. Other top designs are convinced the middle ground (hybrid) is the best path. I believe no one knows until years of data are compared. (Aber was weiss ich, ich bin nur CH.)

Fluid stages depend on the reaction time of the vanes. If they can be proven to reliably operate over a normal lifetime, with quick enough reaction time, then they provide real advantage. But that is not an easy hurdle to overcome, though its use in conventional oil and gas technology has been very successful, and considered maintenance free.

"Life shrinks or expands in proportion to one's courage." - Anaïs Nin