I haven't used it so I can't comment on actual response but the way I see it is that it has 2 eliments to gain and reward customers.
A fiver says you'll refer me and a fiver to your friend to have her cleaning done by me.
Can image it would work well in big social groups.
It's an easier system than the 'fill in a referal form' as there's no paper work, a simple card handed to all customers where as you have to come home an do the letter, envelope and post it and then do them 10sqm for free or something like. As CC we are lazy and need to do no brainer advertising.
Shaun