A couple of additional afterthoughts to complete my earlier post...

The fact that the folds of the hi-flo filter are compressed together on the inside of the filter will make this filter more susceptable to faster blockage than the Piaggio filter. That along with the sticking bypass valve is a concern. Also, seeing more than one source indicating a stuck by-pass valve indicates a quality issue that is not a one-time outlier and this makes you question over all quality. I'd be more concerned about these types of design problems than a less effective filter media which might produce a littler more engine wear vs. a catasrophic failure.

Note also you can't begin to predict the effectiveness of filter media w/o using a microscope to examine the microstructure of the media since you can't see the difference between 20 and 70 microns with your naked eye.