I've followed OXE for a number of years. They've made a lot of refinements and actually the drive may be as unique as the engine itself. The controls are also very nice. The 200 hp OXE is a 2 liter GM diesel (used in Vauxhall, don't know who else uses). It weighs only about 10% more than a comparable gas engine now so a lot of progress there.
The pros and cons based on the information I have and no real life experience with one:
-Less frequent servicing at 2000 hours vs 200 for gas outboard.
-More designed for running at high throttle.
-40% more fuel efficient.
-Comply with NATO single fuel strategy
-Lack of familiarity and proven record, including buyers and mechanics. Yes, basic diesel engine, but nothing basic about the overall outboard.
-Limited models and limited applications.
-Price new is approximately double that of a similar gas outboard. $15-20k more.
For the vast majority of outboard buyers, it addresses problems and issues they don't have. For military applications it makes sense. For perhaps workboats. Even perhaps for an outboard trawler. Just doesn't make sense to throw on the back of a 21' Ranger Bass Boat or a runabout or even a pontoon and that's where the vast majority of outboard sales are.
OXE is by no means new. The company was founded in 2012 and launched the engine in 2016. One thing I do find impressive is that they didn't sell before they had it ready like many new concepts try to. They have used it and proven it in real applications on real boats being used by real people. They've worked through most of the issues although I would still expect some bugs on a new product.