Yes, I have one and it's a bit rubbish really. It's supposed to come on when the humidity reaches a certain level which you can adjust.
It only ever came on when the shower had been running for ages and the room was really steamy. Not much use as I bought it because the humidity level in my house is high in all rooms and I thought it might help with condensation problems.
I've disabled the automatic feature and now just switch it on before I run the shower.