Thanks. I do have a valveless back-up mask but confess that only wear it if going on an overhead environment like a wreck penetration or cavern dive. The valve makes mask clearing easier. I know I should carry a spare but because most of the storage space is taken up by camera kit, torches, DSMB etc, I do not bother to take the second mask as a spare. I should, I guess.
I am surprised that you guys do not recommend masks with purge valves. When I went on a liveaboard dive in Bermuda in 2007, my American buddy told me that they were very popular among the US divers. Also, on a recent trip to the Red Sea, 6 out of 7 Americans on board had masks with purge valves. I guess it was just a coincidence, then.