Does Ocean Master still produce the Dry Snorkel Advanced? The XS Scuba M-line Dry Snorkel looks like the same product. Are there any differences? I have an Ocean Master Dry non-flex) snorkel and am looking to buy a new one. For snorkeling, I have read that I should avoid the flex snorkel. Is there any disadvantage to using a flex snorkel while snorkeling (other than cost)?