I also caved and ordered the 'Folded Corner Ruler' from Bonnie. I used my Corner Pop for clue #3 and I can see that it's difficult to get accurate because it doesn't line up to the seam line. I studied Bonnie's pictures for the 'Folded Corner Ruler' and can see with the lines drawn on it and the direction it's used that it will create accurate cuts. The corner pop is cut from the other direction without a line on the seamline itself to help you line it up perfectly.
So...I decided a Christmas present to myself! And supporting Bonnie for all the work and effort she does to run this mystery. I bought: a Folded Corner Ruler, some Ruler Stickers, and the Seam Guide thing with the little holes in it!
Ho Ho Ho!!