Ducted engines make less noise, which is handy for helipads in cities. They also increase thrust efficiency. If done right, the duct can contain any shrapnel if the fan blades come apart. The disadvantage of a duct is extra weight.
They're chasing the rich-guy helicopter market (think trips to/from/airports) due to the energy density issues of current battery tech, which is going to be much easier without the noise of supersonic blade tips.