Has anybody any experience using a breath controller with an Audya 4, or any Audya product, to control volume or expression?

I have seen that Kelfar Technologies advertise a breath controller that they say has been tested with an Audya, but I can't find any reviews or videos to judge how well this will perform.

http://kelfar.net/bcxp-pro-breath-expression-converter/

I see that several other companies sell breath controllers, but which ones will work with Ketron products, and can a breath controller be used with an Audya 4?

I see that a Ketron demonstrator has used a breath controller with an Audya, so it must be possible, but I am not sure which product he is using or how it is connected and set up to work with the Audya.

Anybody got any ideas? The section to watch is at 3:40

https://www.youtube.com/watch?v=RN2UD2zPNhE