While perusing Subaru materials for a potential vehicle for my SO, I came across the concept of Air-Oil Separators like those made by IAG. Seems Subie enthusiasts swear by them. This seems like a more user-friendly solution than a catch-can as you do not need to empty the thing. On these forums I've only seen folks discuss catch-cans. Is there any reason why? Are there no AOSes available for our cars? Is the functionality of our engines somehow different?