I tried to use this by clicking "show on selected" and entering the url for one of my pages in the url box. It didn't work. I read somewhere else that I should just enter the name of the page, not the whole url, again, no luck. Also tried checking the "single page" box, but it's not clear how I'm supposed to select which page I want.
I think some instructions w/the widget or on its home page would help. This doesn't seem to be very intuitive to me.