I agree with the poster that mention that it's disingenuous to state several times in the description above that it's free yet there is still a cost to remove the watermarks. Yes, the download is free but it properly falls into the "demo-ware" category that has been used by developers and best understood by users for many years. labeling it "free' rather than "demo" is very misleading and I for one will not even download it.
Incidentally, for the same price of the "pro" version you can go to the MAS and buy Apple's Pages, which does a real slick and easy collage, one where you the user has total control over the positioning, rotation, and sizing of your photos. This app takes a bunch of photos and creates a melange, not a collage, with photos overlapping each other covering parts that you might really want to show. Plus with Pages, you get a few other bonus features!