A helmet should be capable of protecting your head on impact. Nothing more and especially nothing less. So based on this requirement you would always go for the full-face helmet used by downhillers, because it protects the largest area of your head. The reasons for choosing lighter helmets are just ventilation and a lower risk of injury based on the type of riding you do.
On an Enduro helmet you ditch the front part of the helmet because you don't do extremely hard downhill tracks and such big jumps where you can expect unreasonably high forces on impact, and you also need more ventilation on the uphills. However these helmets still cover a larger area on the back of your head! On a road bike you don't expect a crash on rough underground and for flat roads, a lighter road bike helmet is sufficient. If you look closely these helmets do cover less area on the back than usual mountainbike helmets.
This would imply a safety ranking like this: Full-Face > Enduro > Road Helmet
You can use the mountainbike helmet for commuting without any worries, just be sure you don't to the opposite. I even used a snowboard helmet for mountainbiking: The covered area is pretty similar to an enduro helmet, the safety standards are even higher because these helmets also have to work in cold conditions. However there is less ventilation which is why I will probably buy a specific enduro helmet.