Yes, I demonstrate it in class every time. It works very well. At first the class was concerned that it would deploy during a race if the pull tab got mangled/pulled in the starting melee of the race (which would be a funny sight I think). But no, you have to really pull on it.
Of course it must create some drag but it doesn't seem like much since it is tucked in under your rear..It is a cost/benefit thing. I personally wouldn't race with it because I am a very confident swimmer, but I wear it for open water practice all the time.
Instruction for New and Nervous Swimmers in Irvine, CA
Ironman Series Books "Fearless Swimming For Triathletes
(Meyer & Meyer 2011)" and "Functional Strength For Triathletes (Meyer & Meyer 2012
)" and others