^^^ Hey Robin.
In answer to your question - the stage one version does not filter and catch any oil vapors like the catch can does. It is simply a stronger version of the OEM PCV which can be prone to failure.
Thats not at all true. In fact, its 100% incorrect.
It completely blocks off the PCV outlet, retaining just the return line to the sump. And comes with a block off cap for the inlet manifold on the PCV inlet.
The Eurojet fix does what you describe (with an uprated check valve), but the BSH fix is much better removing the PCV from the equation completely.