Respiratory training products . . . Are they worth it?

Some time ago i was introduced to a peculiar looking bit of kit. It reminded me of a scuba regulator but as far as i could see it didnt do anything. Then I was told that it was a ‘Powerbreathe’ respiratory sports trainer. ‘Oooooooooh’ I thought to myself. The words ‘respiratory’ and ‘trainer’ rang hard in my ears. Could this …