Polarizing filter – degree of polarization vs spolarising sunglasses?


I thought a polarizing filter only lets thru light of one polarity.

Thus if I have 2 polarizing sunglassses and look thru both superimposed and rotate one it should completely block light at 90 degrees rotation. I’ve tried this and it works.

However, I have two of Massa lens polarizing filters and they only slightly reduce the light when thus superimposed and rotated. I complained to Massa and they claimed two superimposed filters rotated 90% should block the light.

Looking on youtube I saw that viewing the filter against a computer monitor, it will block the light completely when rotated if it is a good filter eg Hoya filter was shown to do exactly this.

Does this mean that the Massa filters are defective? If not, are many so called polarizing filters (other than Hoya), this bad at polarizing compared to polarizing sunglasses or can I get ones that polarize 100%?

I checked a similar topic but it does not look at the degress of polarizing affected:
How do I choose a polarizer?