Wasn't sure how they would work and thought that if they didn't, well, nothing ventured nothing gained, but I was quite pleased with the results. On the two black pieces below I've watered down some gesso, painted it onto the stamp (you could just stamp into as well) and randomly plonked it down wherever I felt it needed something. The first one I've used the square stamp.
The one below I've used the rectangle one and just stamped around the edges. These pages are 30cm x 30cm so the whole page doesn't fit in my scanner. These are unfinshed pages, they will have a lot more stuff added to them over time.
The one below is a canvas about 30cm x 30cm that I've painted a few shades of green (what else) and I used the rectangle stamp along the edge.