The cost of the Arneson ASD8 in-line drives for the Yanmar 440's is $13,655.00 ea. complete with the hydraulics, external hoses, backing plates, mounting bolts and trim pumps. You will need a marine gear but you do not need a boat specifically designed around the outdrive.
Every I/O has O-rings and pumps so I do not feel we are making a maintenance nightmare by using them also as there are more than 1000:1 I/O’s to Surface Drives out there.
Slow speed maneuverability is far better with a drive that can vector thrust as you do not rely upon the accelerated water effect over a rudder.
Fixed surface drives are nothing new. We made them back in the early 70's ourselves and abandoned them in favor of something better. I’ve got an old, old by my standards, book on performance boating published in 1948 and on the cover is an Alfa Romero boat with twin V8’s and fixed surface drives. The engines were staggered too. Basically they are just a ski boat drive system mounted on the transom vs. under the bottom.
As far as jumping off the transom and landing upon a propeller, we have made propeller guards for this situation.
Choose what ever drive you can afford, fits your boat and can live with. Someone can point out all the negatives and positives of each option so you will need to weight all these factors, large and small, out to make a wise decision.