After I got tired of having my snorkel get tangled in my gear (not paying attention to what I was doing?), I starting diving with a collapsable that I kept in my pocketl. When I needed it, I could usually get it in play--but not always, particularly in rougher seas when I needed it most (bobbing in the ocean, waiting for the boat to see this drift dive is over. By the way, where IS the boat? Where did these waves come from?).
When I did my rescue course I started using at real snorkel again and returned to the faith for two reasons:
1. I snorkle daily in my pool this time of year. It's good excerise, and it's more fun cleaning the thing with a net and mask than with the plumbing (the underwater thing, you know). And doing a lot of snorkeling even in calm waters, I get a good sense of the flimsy unreliability of the collapsables compared to the purge models. Real snorkels are fun and reliable. Collapsables can be work (flood, choke, gasp).
2. More important: This is SAFETY equipment. Why cut corners?
Of course you don't swim backwards with a snorkel, but when you need it, say in the ocean or the great lakes or even when tired in a quarry, I'll use a snorkel, preferably a good one, and hang it where the experience of generations of divers says it should be. Like most safety equipment in most dangerous tasks, there's a reason this is done this way.