Great sound, bad design/fit
I purchased these headphones to use while running and working out. I'm a big Sennheiser fan, and the sound did not disappoint. The headphones were fairly comfortable, and seemed like a decent fit for regular wear. However, when I wore them for running, even at relatively easy paces, the fit became an issue. I tried out all the different earfin and earbud sizes and combinations (3 sizes of each provided), and settled on the combo that seemed totally secure. However, as you can see from the picture, the controls on the headphones are fairly chunky, and there is another similar sized block on the other side of the headphones to balance this out. Added together, these are relatively heavy and bounce about while running, and this constant bouncing serves to pull the earbuds out of your ears. There is a slider you can use to help tighten the cords to the back of your head, but even when I did this, I was still experiencing the bouncing that constantly tugged the earbuds out. As a result, I had to reach up to push the buds back in every couple of minutes. Not very desirable for an hour-plus run. Ultimately, I returned these. Bottom line--even if you can find a good solid fit on these, the design and weight of the controls seem like they'll lead to similar fit issues. If you plan to use for running or similar intensity activities, I would consider something else.
Pros: Great sound. Comfortable, decent fit for non-athletic use.
Cons: Bad fit for athletic use, especially running.