As both a diver and a snorkeler, I'd say that the underwater walking is different from both (just as diving and snorkeling are different from each other). When snorkeling, you have the wonder floating sensations that are unique, but when diving you can stop and examine something more closely either on the bottom or on the side of a formation of some sort. That's hard to do when snorkeling and underwater walking should allow you to do that to some extent. Diving also is special because of the fully 3-dimensional aspect of it, unlike anything else I've ever done. You move about in 3 dimensions, like a fish or a bird and neither snorkeling or underwater walking allow that. Of course, scuba requires more training and that can make it less relaxing for somebody, like myself, who doesn't dive very often, so for relaxation, nothing beats snorkeling.