Dry snorkels are definitely the goods. For those who don't know, they have a one-way trap. When a roll comes over your snorkel or you go down, it shuts instantly, preventing water from entering the tube, so you rarely have to purge much when you surface. It's more of a convenience feature if you know how to purge, but it really helps those that are new to it.
I ran into a lady trying to teach her very young daughter how to snorkel in St. John last year. I was returning and saw them struggling with the water she kept inhaling because she couldn't purge her rental snorkel well. They were staying at my resort, so I swapped the mouthpiece with my spare and gave them the snorkel for the day and they couldn't thank me enough.