Pros: Great sound stage, very good resolution, perfect fit, nice design, good cables..
Cons: A decent amp is mandatory.
I ordered the Hifiman HE-4s to upgrade from my AKGs (701 and 240 Studio). I was a little concerned about the amp requirements but I'm very pleased with the performance of the AMB M^3. The cans fit perfectly, the sound stage is very large, the resolution feels better than with the 701 and the bass is simply amazing. Great fun, even at low volumes. At the beginning I was a little deterred by the agressive treble, but this got better after a couple of hours, maybe because I just got used to it. I listened to a lot of different stuff: Jazz, Classic, Electronic, HipHop, Reggae. Even though the phones are not on the analytic side, it's a joy to listen to classical music, especially piano.