I actually have a couple of these. The do a good job of reducing hose size well maintaining good air flow. I use it to hook my bench top band saw and table saw to my dust collector. I also use one to connect my contractor saw to my shop vac when I have to move it away from the dust collector. I have a small shop in the basement and a larger one in the garage, and sometimes tools end up being used in the other shop, or outside. So I need to be able to change between 2-1/2" and 4" dust collection.