Well, one thing for doggone sure, it does NOT eliminate blowby. If anything, it increases blowby by decreasing the atmospneric pressure in the crankcase.

It may load the oil rings more and thus increase their efficiency, but blowby doesn't come because of the oil rings. Blowby is when the compression ring isn't sealing well anymore. Generally this causes the oil rings to flutter or unload, IIRC. But the blowby starts at the top ring.

I found out about leaks when my PCV hose was blocked, engine leaked like a sieve. So returning the PCV to operation eliminated most of the leakage.

The PCV circuit would lean out the engine at idle, so the valve is closed at high vacuum and opens at lower (loaded) vacuum. This other contraption depends on the crankcase being sealed to avoid leaning out at idle. The only air coming through the hose would be air that leaked into the engine.

The contraption could be problematic in that depending on where the hose is plumbed into the intake, one or more cylinders might become oil fouled from the vapors. I had this happen with a leaky vacuum pump which would leak oil into one runner of a six cylinder, but only on steep downhills. It'd literally cover the road with smoke. That one plug could oil foul in 10 minutes.

R.