Both are very nice masks and have their perks.. eflexes take any Vents lense, have nicer ears, have very puffy foam and great breathability. Profelxes are more customizable than eflexes, have decent ears and lense. I prefer my eflexes over my proflexes but both are great.
Yea ears and head shape is the big difference if you have a small, medium, or large head you can get profiles cause you can change the strap. Also my friend makes his own flex ears so I him make me a pair and they are way more protective and way easier to hear. The eflexes are for a big head. I prefer flexes