My first equipment was an older Impulse I snorkel (non-flex) that I bought at a garage sale. So, in preparation for a snorkeling trip, where I wanted a spare, I bought a new Impulse II snorkel. I thought the "flex" model would make it nice for those times when, at the surface, I would remove my snorkel to talk to friends (because with the non-flex you have to kind of wrangle it out of the way).
But, when I used the flex snorkel, I found I did not like it. The reason was because, as I was swimming along, the water streaming past me would wobble and bend the flex section, causing a constant pull on my mouthpiece and fatiguing my jaw. I returned that snorkel and bought a non-flex Impulse II instead. I would rather deal with the slight inconvenience at the surface than a constant annoyance while I'm actually snorkeling.
I don't know that others would experience it the same way, but I thought I would let you know what I found.
I do like the Impulse design for snorkeling (non-flex). I have switched to a more simple and streamlined snorkel for when I wear it SCUBA diving.
