These things rock!
I use them all the time when I go for walks. They don’t block you ears, so you can hear the traffic around you. Also they are really comfortable.
The only downside is that I will sometimes wear these at work and forget I am wearing them. This has lead me to forgetting that the person I am talking to can’t hear my music. Luckily I am more amused by this than embarrassed.
Oh and if you want them to be noise cancelling, wear ear plugs with them. Since the sound is travelling through the bone, ear plugs don’t affect the headphones.