Using a full face mask is a great alternative to a standard snorkel mask for three main reasons:
Visibility – gives a clear uninterrupted 180 degree view. The frame seals behind your vision line, which means you don’t have a frame that alters your view.
Water barrier – the mask seal around your entire face, which decreases the chance of water getting into the mask. The rear strap holds the mask in place on your head, allowing you to move freely.
Natural Breathing – While using a full face mask you can inhale and exhale through either your nose or mouth. The natural breathing helps keep you calmer and more relaxed in the water. The absence of a mouth piece, also make extended snorkeling more comfortable, allowing you to snorkel longer.
Safety tips when using a full face mask:
Make sure that the mask you use seals properly around your face.
A full face mask must have a dual airflow system with a one way ventilation valve to ensure there is no CO2 build up in the mask or snorkel.
A snorkel mask is designed for recreational use only, just floating on the surface and comfortably looking down
Never use it for extensive open water swimming, free diving or swim practice.