They work well (I used them on an mp3 player and my laptop), but they have an unpleasant feature: the headphone cable is a very foul smell (to say things more clearly, it really stinks cable). You do not realize outdoors, but the smell of this cable is very noticeable after a few minutes in a closed room.
Of the 4 headphones or earphones I bought these two years, is the first time that I come across such a case. I tried to have an exchange with France sennheiser about it, in vain. I did not cast (AC will soon) but I no longer use my earphones MX 550.
In view of the fatally flawed, I consider the price / quality ratio is bad (unless it has a stuffy nose). I give 2 / 10 to 550 MX: from sennheiser, I expected a more serious control of the materials used.