I have not had any personal experience of these, but have seen a number of videos on YouTube about them. One of the most surprising elements of them was the noise generated; admittedly not the same as a two-stroke but unexpectedly high.
Looking at the experiences of those people who have used them, they seem more suited to those taking short trips or fisherman using them for trolling. Not too sure the technology exists yet to provide the range for cruising or suitable power for emergency use, (at least not without additional v/heavy batteries).
I wonder if any places are offering trials??