The one thing I don't like is how the manufacturer claims the crankcase is "under vacuum" in most driving situations.
The only way this can happen is a highly restrictive breather filter is fitted, or an undersized (about 1/4 id) breather hose is connected from one valve cover to the aircleaner.
Then at anytime the engine is loaded the crankcase cannot be vented correctly. It may well not leak while idling/cruising, but will certainly leak under load.
High Performance PCV Valve Shootout – Flow Test Results – M/E Wagner Performance Products
Gary