There is no reason to use MM4 unless you're interested in beta testing, but there's also no reason not
to use the Discogs tagger if you are using MM4. It works fine once it's installed, and it's far and away the best tagger available for MM3 or MM4.
MM4 is very close to being a Release Candidate, so it's actually quite stable. With the latest updates, it's much quicker than MM3 ever was, and gives me fewer problems and crashes as well.
There's no better way to put MM4 through its paces than by using it in my everyday music management--and that heavily involves the Discogs tagger at this point. not only that, but it also helps to test the plugin interface. Now that I think of it, I can't think of many reasons not to use the Discogs tagger... but to each his own.
Thanks for making it regardless