The stock PCV has a check valve that, in my mind, is plenty good. I think an additional check valve is unnecessary unless you plan on going over 20psi boost. Adding one between the manifold and the can will keep pressure out of the can, but that's not necessary if the can is of at least decent quality and the hoses are clamped properly.
The VTA (vent to atmosphere - the filter on the fresh air tube) isn't emissions legal. Any state that does a visual inspection under the hood may notice that and fail you. The longer term problem is oil mist WILL occasionally come out of there. The classic car guys that do that on their breathers usually wrap a rag, sponge or similar around it to catch the oil before it makes a mess.
I'm not a fan of the single can. Doesn't make sense on how you can set it up properly. Those multi-connection cans are set up with a single "clean" air connection and two "dirty" air connections. When suction is applied to the clean air connection, dirty air is pulled in through the other two connections, goes through the element(s) and cleaner air goes out the clean connection.
A PCV system has two components - the PCV that provides crankcase vapor to the manifold, and fresh air intake (usually on the opposite side of the engine) so the air circulates through the crankcase.
The main catch can goes between the PCV and the manifold, with the manifold on the "clean" connection. Whenever there's manifold vacuum it'll pull crankcase vapors through the can and through the PCV valve, with the can catching the oil that will be suspended in there.
The secondary catch can goes between the fresh air tube and the intake tube with the intake tube on the "clean" connection. Whenever there is more crankcase vapor than the PCV can handle - which on a turbo car is just about every moment the car is under boost - crankcase vapor will be pushed out the fresh air pipe. It can't go in the manifold because that's pressurized. That crankcase vapor going out the fresh air pipe has oil in it, just like the other side. Previously that dumped straight into the intake track, so we're right back where we were before. Now you want that crankcase vapor to enter the "dirty" side of the can, then the clean side goes to the intake tube so the car just burns the leftover crankcase vapors (some oil will be left, plus some gas vapor, plus combustion byproducts). Putting a filter on the fresh air pipe will just cause oilly air to be sprayed all over the front of the engine every time the car is under boost.
Anyway, the whole point is air has to circulate *through* the crankcase. We figured this out in the early 60's. Every single OEM PCV system has had the same setup since then. With a single can you end up applying vacuum to both sides of the engine. Sure, you pull out the crankcase pressure and are emissions legal, but you don't circulate fresh air. This leads to the oil failing earlier than it should.
FWIW, the $30 Amazon cans are actually quite good. I added a wad of steel wool (and filter material to keep the steel wool out of the engine!) to help out the sintered bronze filter. The price of some of the cans out there really makes me wonder, especially with the limited info about the internals.
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