I have a pair of these & use them fairly often. In regards to your concerns:
1. Yes, you can hear music and the surroundings quite easily. They rest over your ears, so they do not drown out the "real world" &
2. No, they are not so loud that anyone can be bothered by them. In fact, unless someone is right next to you, they cannot be heard at all (even if then).
They have a slide volume control on them that allows for adjustment without having to screw with your mp3 player while working out.
The only real issue I have with them (other than the price!!) is that it is a bit tricky to get them where you actually want them. They hook over your ears, so you have to kinda' play with then to get them to stay where they are comfortable for you. The earpieces do bend, so they can be fitted for the individual.