Well, in 14 years of avid diving
, I don't think I have EVER lost
a mask or snorkel - and I do like using my snorkel - for snorkeling! I also never touch the wibbly wobbly rolly uppy snorkel that I keep on my BCD pocket to meet standards, because I like a good solid snorkel for snorkeling!
I have regularly free dived to 14m to recover dozens of masks over the years - mainly because of idiots who take them off their heads before they are back on the boat. If they would listen to me in the first place, and put the d&*n things around their neck (if they really want it off their face), they wouldn't lose the d^&n thing in the first place!!
I do find having neoprene strap covers on them does help to slow down their descent!