Gives you the benefit of both the upcut spiral and the downcut spiral in one cutter. These cutters are great for faster feed rates when you have a laminate on both faces, or for when you are routing composite woods. One thing to note is that the up/down spiral is a 50:50 ratio. If you don't cut down at least 1/2 of the CEL through a material you will not receive the benefit of the compression, try the Onsrud 60-100 mortise series.