The build & construction seems rigid and durable, it has withstood some wear and tear without indication of problems.
For example it's not very easily affected by slight accidental pulling of the cable, which inevitably happens during normal use.
These are the best earphones I've ever owned, and with proper use they will probably last decades.
The sound is nice, loud and clear. I use it in my home studio recordings and I hear bass, mid and high frequencies very good.
They deliver accurately what the sound signal contains.
They don't have noise. The reason why you can know this, is even if you turn up your volume very high (without sound input) you don't hear noise.
An obvious choice for any professional and I don't think you can get a better pair of headphones in this price range.
AKG has impressed me.