Bought a Met Parachute a few years ago. They're a good idea, and surprised more manufacturers have not developed something similar.
I didn't buy it thinking that it would replace a full face helmet, and simply just wanted a little bit of extra protection to my stunningly handsome features (not). I found it a bit uncomfortable, chin strap particularly. Very good airflow through the helmet though.
I wouldn't buy another one, but would consider something similar, of better design, if it was available.