I was introduced to this back in 2002 for a course run by one of the BFAs, and I still plough up and down a lane in my local pool doing bi-fin exercises taught to me in sessions run by the other BFA.
As a heavy boned sinker, I find it so useful to be able to breathe with my head down.
Apart from having to change the head strap a couple of times over the years, it has now served me totally reliably for 20 years.
Magic.