I usually avoid discussing stuff on for-sale ad but in this case I make an exception as it has already turned into a discussion thread.
This is a great thing to have for those who need to cut their own mat. Even if you don't (have to), it doesn't take long to make it a worth while investment. A full size sheet costs about 12 dollars. A window cut 16x20 mat costs about the same if you have someone cut it for you. If you do it yourself, you can get FOUR for price of one. Personally, I standardized on few colors but my sizes vary a bit. So I just order a bunch of sheets and cut them myself. In about a year, I saved enough to pay for the cutter.
I apologize to OP for intruding on his for-sale ad.