Johnathan, I haven't used one yet but would consider it. I've had a bit of an insight into how they work as they were developed by one of the lecturers on my Sport Science course, and another lecturer has done considerable research on them. As a result we have been required to read a fair amount of research on them and the science behind them make sense. Both the lecturers are people I respect and they certaintly believe in it. However, as I say, I haven't used one myself, so I would be interested to know how you get on.