Excellent, but sadly this product has been discontinued and is very hard or impossible to find. The headset is extremely lightweight and is designed to be worn for a long time in roles like air traffic control. When available they cost about £40.
The reason to buy this product is that it is the most comfortable headset I have used. I use mine with Skype. You certainly can wear them for extended periods. They fit well, are highly adjustable and have low spring pressure on the ears. Ideal really!
The sound quality at the stereo headphones and from the noise canceling microphone is first rate. They are pretty robust too. I have dropped mine onto a wooden floor many times. Sometimes they come apart, but always snap back together with no lasting damage.
I think Sennheiser should reintroduce the MAB 40. The name is written M@B 40 on the headband.