I don't have their tool, but used a laminated instruction card from Fons and Porter. The method on it is called "lumpless finish." The angles were confusing the first few times around! Still, the end result was perfect, so it was worth persevering.
You're folding both tails of the binding back on themselves at the 45 degree angle to find the sewing line. I'm pretty sure that is what the tool from MSQ is going to give you. Make sure you test your binding before cutting those tails off - it's easy enough to rip out a short little seam and redo if needed, but if it's been cut off and you turn it out only to find it doesn't fit... Well, that'd be sad!
Try a search for "lumpless binding" or "lumpless finish;" you should find several tutes on it; hopefully one of them will make it more clear for you. Good luck!
Last edited by peaceandjoy; 08-15-2013 at 03:37 PM.