If you want to find out how it sounds, just grab a sample of the material (various people make them, DaLite, Vutec, Draper, Stewart) and drape it over your tweater. The high frequencies are affected most, so this should be a decently accurate simulation.
Stewart's Microperf is really the high, high end of perforated screens. It's the only one with THX certification (it had better be certified, because THX helped develop it) and the associated licensing fee. I believe it is also the only one that comes with an EQ (as part of the certification). Obviously it all kind of adds to the cost.
With EQ, most people should not notice any difference in the sound. There may be some highly attuned audiophiles that could tell the difference, but that's not really my province. You may be able to get them to send you an EQ and a sample to do a test, Stewart's usually pretty good about stuff like that. Talk to your dealer.