Cons: Outdated Sound, Microphonics,
Like many other people, I got my cx300's as they were widely available on the high street with not much competition at the time. They are mostly known for their bass which is very abundant. The problem with that much emphasis on bass is the rest of the range suffers. Treble, in particular, suffers quite badly and is drowned out. Add to this very little clarity in the bass which doesn't have great extension anyway and for sound you are soon left wanting.
The trusty cx300's are quite comfortable to wear but isolation is not that good due to the shallow insertion and cable noise can be quite bad. You just get the feeling they were designed for a 13 year old who just thought more bass was better, people's ideas have moved on since then. Overall there are much better for the price out there. Also there are many fakes out there which are worse but come without a warranty (which you may need).