I purchased this headset to use at work. Under normal circumstances, I can only use one side at a time and the environment is noisy, so that is definitely a consideration.
The sound isolation is pretty respectable when the earpieces are fitted in the ear snugly. The earpieces sometimes slip out, but never fall out completely; it comes with a few sizes of earpieces so I am trying new ones to see if that solves the problem. Even when they are only partway in, I can generally hear them well enough, but because I mostly listen to classical music and soundtracks at work, I have to have the volume near or at maximum.
The sound quality is fairly well-balanced and clear. It might not be quite rich enough for the true audiophile, but if you just want to listen to something while you are at work or chilling in the library, or trying to drown out a noisy public place, it is perfectly sufficient. If you need to use it with only one earpiece in like I do, note that, at higher volumes, the music can be heard outside of it, which could be distracting to others if you are in a quiet place.
Note that it has a built-in speaker, but the speaker is not very loud and is only located on the right side of the headset. The speaker also drains the battery faster, but even so, the battery life is pretty good and should get most people through their workday (if that is the intention).
The headset also has a microphone. I have not listened to the audio coming out on the other side, but I have been able to talk on the phone in noisy environments without the person on the other side complaining about the noise, so it is up to my standards, at least. I can talk fairly quietly and it still picks me up enough for the other end to hear me.
As far as comfort is concerned, I barely notice it when wearing it all day. In fact, sometimes I forget to take it off when I get home. If I run or jump, though, it bounces on my collarbones, which leads me to believe it was really not meant to be used during physical activity (luckily, I have another headset that was). I sometimes carry a messenger bag and the strap slides underneath it, which can cause problems with it trying to come off your neck when taking the bag off your shoulder.
The wires leading to the earpieces are really thin. I have not had problems with it, but I advise against tugging on them too hard, just in case. They retract easily when tugged gently. The wires are long enough to reach my ears and barely any longer--again, not likely designed for use during physical exercise as this can cause them to get tugged out when the unit bounces around.
The unit has several controls, which can be rather useful. It has a separate button for starting/pausing music playback and answering calls (which mercifully triggers voice commands when accidentally pressed instead of calling someone), as well as volume controls, forward/rewind, and physical switches for power and switching between earpieces and speaker (which it does seamlessly).
Overall, this is a pretty good headset. I might debate that the standard price point is a touch high, but it was an excellent deal when on sale. When I am not sitting at my computer or out for a run, this is my absolute preferred headset.