[glennv]

We from Apnea Academy also teach to focus on closing the airways underwater in favor of ascend speed.
I like Sebs ideas about the mask but have serious concerns about safety issues with underwater blackouts without the mask on (an extra possible passage for water into the lungs and as stated before and well know fact that this seriously complicates a successful recoverie). So comparing the pros and cons I would never suggest removing the mask underwater in case of difficult ascends . Rather dive without mask and use a noseclip instead. (or liquid goggles etc.) This way at least the open nose passage is closed off.