not for everything, but great at what it does
It's supposed to be a measurement microphone, but I love my M30 for recording.
This is an incredibly accurate microphone, which is simultaneously a good thing and a bad thing. Whatever the source sounds like is what you hear on the recording. If you have a good room, a good instrument, and take the time to find the right placement, this mic will make all the difference in getting a great "you are there" sound.
But one downside is its clarity. If either your room or your instrument sucks, the M30 will make it glaringly obvious.
Also, the mic's sensitivity can be a drawback. I used it for a drum overhead one time (of many), and kept hearing a "breathing" noise between takes. The noise nearly drove me crazy as I tried to figure out what it was and where it was coming from. It turned out to be the M30 (positioned at four feet over the drummer) picking up the breath of the drummer. The noise floor on this mic is very, very low. It allows you to hear the smallest amplitude noise clearly.
The M30 has no coloration. The frequency graph for mine has a variation from unity of less than 0.2 dBu across the spectrum (up to 22kHz). There is no "hype" or "thickness" or "grain" added to your sound. What's there is there, as far as sound is concerned. If you want "color", use a different mic.
But now that I've complained about clarity, sensitivity, and a lack of coloration, those are the reasons I keep reaching for the M30. It works well as a drum overhead, vocal (at a distance!), acoustic guitar, strings, and piano mic.
Bottom line: a great mic, but only if you have a quality source and a quality room. It's not my "desert island" mic though, which is my only reason I can't give it a full five stars.