The leak was a little high, but I think I know the reason for that. It seemed that, as long as my mouth was open and my cheeks were full of air, the FullLife sealed very well. When I closed my lips to swallow or moisten my teeth and gums with my tongue, it broke the seal for a couple of seconds; then my cheeks puffed out again, and all was well. I'll turn up the humidifier tonight to try to combat the dry mouth and see if that makes a difference.
Otherwise, the mask was comfortable, with the exception of the pressure on the bridge of my nose. I'm sure that's just a matter of not being used to having anything pressing on my nose, and I felt congested as a result, so I'm sure I mouth-breathed all night. But at least I wasn't losing therapy.
The sizing guide was part of the white bag it came in. I cut out each one, scanned them with a black background, and uploaded them (here) so I could post them.
Keep in mind that the mouth needs to be open for proper fitting. If you want to print and actually cut them out, make sure the pic is at 100% and fits a full sheet of paper. If you just want to wing it and cut out your own, the measurements of the openings are as follows:
Small:
Height 3 1/4"
Width 2 13/16"

Medium:
Height 3 11/16"
Width 3 7/16"

Large:
Height 4 1/4"
Width 3 3/8"
