I run those in my collectors and I have Dynomax Bullet mufflers. Before I started using them some oil would come out of my breathers while I was going done the track and get on my headers. I was not running a pcv valve. I do not want oily air going in my intake.
I have only installed one so far and it stopped the problem, I may not ever put the other one on.
see this is exactly my same problem. I had breathers- three of them and one filler cap. oil is going all over my valve covers. & I didn't want to run oily air into my intake so this could be the compromise to only use one and not both?