I got this pretty late for my build, but it created a noticeable difference in the reaction of my engine when I put down on the accelerator. I'm pretty sure its a catch rather than an air oil separator because it doesn't have an outlet to return the oil, however cusco makes another product that is called a catch can that is cheaper than this one. The build quality is really nice and its a pretty easy install, except the instructions are only in Japanese, though the pictures and google translate are enough to get by. I do wish it came with the pop clamps instead of the screw clamps for the hoses, I just prefer that look. Overall its got a nice finish and looks beautiful but also is really helpful for performance.