I've got a PCV valve on mine, and the mini-filter blows no oil at all. I only used one because there's no graceful way to hook a hose from the filler cap to the air cleaners I've got on the dual Webers.

Here in the Northwest, we have problems every winter with the hose adapter that goes between the two-bolt air filter and the forward SU. It's so wet that the adapter fills with condensation and eventually causes the carb piston to stick. That's a candidate for a mini-filter instead. No such problems with the three-bolt filters and their built-in hose fitting.

I just recommended a mini-filter to a friend with a supercharged 1800E. No graceful hose connection in his case either.