I was going to buy the Prosharp, but when I put it in the cart the cost went to $79 when you included their shipping. So, I went with the $30 edgechecker on ebay (the rainbow striped one, the lower link). Mistake. Looked like it cost 25 cents to make. The back piece measuring gauge was glued on 2 or 3 mm crooked. The magnet portion of the back piece was clearly not square in the least. It's only about 2 inches long, so the inaccuracy stated render it totally worthless. Sent back. A measuring tool needs to be accurate, or you might as well not even use one. I just bought a Wissota 911, so I may have to spring for their $99 Elite version.