Swamp Rat,
Having a purge valve in my primary mask would always be a concern--minor, to be sure, but an in-the-back-of-my-mind concern nonetheless. I've tried them and don't care for them.
To sum up my experience with purge valve masks:
When the lake/river/spring bottom is stirred up, it seems some of the tiny particulate matter will end up stuck in the purge valve, and seepage results.
And, as Tom has suggested, ocean salt water in the eyes will become a significant irritant, especially if you are in the water for any length of time.
I know masks have been improved a great deal in recent years, but when mask clearing becomes second nature with experience, why have a built-in failure point. Not to mention the extra cost . . .
Warren