K3 & waterproof Pentax remote O-RC1?

Apparently the K3 works with this remote,BUT not the fn button on it. What does this button do? Thanks.

The fn button works the camera's autofocus (successfully!)

Thanks John. What a shame it won't work with the k3!

Sorry, forgot the O-RC1, has three buttons, was thinking of a third party remote that only has two.
As you say, the Fn button doesn't seem to do anything but apparently it does do something with certain point-n-shoots (sorry, no idea which ones.)
The middle button (the button with the trees on it) definitely does work the auto-focus, which is what I incorrectly presumed you were referring to.

Thanks, I will consider getting it.