His precise, rich bass, high quality finish. Recommended!

At his, the look-ear provides deep bass and a good attenuation of ambient noise (but not a complete attenuation, which I appreciate for safety reasons in the street). The highs are precise without being garish; I have also been compared to CX-200 Street, sounding a bit muffled with bass slightly too present for my taste.
By using a Sansa Clip Plus rockboxé, I get a nice sound with a small boost of 3 dB in the bass.

At ease of use / strength, satisfaction is also the rendezvous.
The cover provided is very convenient for transportation, provided to wrap the cable itself by rolling between his fingers at every turn (thus avoiding making a twisted form). I can even put my mp3 player there to slide all in a pocket.
The silicone tips are very comfortable, either to listen in a quiet place or take a jog.
However, the cable rubbing against clothing is heard in the headphones because the sheath is made of non-slip rubber. The problem was quickly rectified by adding over the kind of tweezers that are usually found on mobile phones free kits. Sennheiser also provides with some more expensive models and would benefit from it with all his headphones, given the low cost price of such an accessory.
From the viewpoint of the strength, I have no complaints despite the negative comments I've read everywhere. My helmet running smoothly for over two years, despite several jogging in heavy rain and a year in Australia. I just take - mostly - the precaution of transport in the cover provided when I put them in a pocket or bag. I've had no problem of false contact and sheath holds up.

In summary, I do not regret having put a little more expensive and have preferred the CX 300-II in the lower models, they accompany me everywhere and reproduce with a good drive and good files encoded sound very pleasant.
Beware though for those of you who do not have the habit-ear: the sound pressure higher tired faster ears - so take breaks ;-)