I don't speak from personal experience since I don't own one and never would consider it. My opinion is purely based on what I've read in the boat rags, plus never having actually seen one on the water.
The first one I saw was at the Miami boat show. Later shows in my home area turned up not even one. As I understand it, the design was specifically to address wake surfing. Thus, right off the bat there is a limited market.
The last article I read commented that the sales were not as hoped. I would imagine that sales might be area specific, so some areas may have sold out while others may have been dismal. Because of limited sales overall, the writer questioned why Mercury would develop one as well.
Safety is often cited as a concern. Again, not my data, but it is often cited that that duoprops may present more safety concerns due to entrapment. Having the props far up under the boat could possibly cause entrapment to be more fatal.
No horse in the race - just providing some info. When you buy a new boat you need to investigate all angles. Personally, after switching to an EFI Outboard, I'll never go back...