I've worked with a MG II filter set for about 8 years. The filters came with my most-used enlarger (Durst M800). They did a fine job with different brands and types of MG paper.
Then I read this thread earlier this year and decided to replace the MG II filters.
Well, in the grade range that I regularly use (1-2.5) the new filters work the exact same way, judged from the prints, with a not so scientific eye.
There may be a visible difference at higher grades, I have yet to try.