as a new owner of the M5's.. I have to recommend them wholeheartedly. They're the sound signature I was looking for, and thought I had with the E4's.
Very detailed and impactful bass. They give you that feeling of vibration throughout the rest of your body, but they remain in the background where they belong and set a good foundation for the rest of the music. Mids are present, neither buried nor overwhelming (which the Shure E4s' were) and the treble is indeed not sparkly, but gets the job done in terms of detail and non-fatigue-inducing. I've been listening to my pair for the past 2 hours and I have stuff to do, but can't make myself get off my chair!!
Comments on these phones are spot on. They aren't the most detailed phones compared to the dynamic armatures, but what they get right is the smoothness and the actual experience of listening. It's not to say they aren't detailed at all; they're about 80% of what the E4s had, and it's a conservative estimate. It's like being immersed in the music as opposed to having it shoved down your throat like other phones do.
For those who didn't get a chance to find this in a different thread. One of the users around here spoke with a music professional, and he did prefer these phones for on-stage use over more expensive IEMs because of their lack of fatigue.
But in short, I'd say that while $130 is a stretch for some people to pay, I'd say this phone would please the sonic tastes of many. So get in on this bandwagon!!