I had one for my Canon New F-1. It can use the smaller Fuji pack film, which I generally used even when there was Polaroid.
You can get two exposures on a frame. It's been a while, but if I recall correctly, there is a measuring strap, and you pull out the white tab to the end of the strap (line up the end of the strap with the end of the tab, hold both together between your thumb and forefinger, and pull until it stops) for the first exposure, then pull it out the rest of the way for the second exposure.
I posted a sample exposure taken on Type 669 in this thread a while back--
(there was a url link here which no longer exists)