I purchased the Sony headphones for watching YouTube and TV etc on my laptop so wasn't expecting much.
I tried them first on my phone and was immediately impressed. However after connecting them to the more powerful output of my laptop the headphones really came to life. They produce a slamming bass when called for and a relaxed treble which makes for easy listening especially on albums like disclosure settle. I then compared them to my sennheiser MX500 in-ear headphones and the difference was like night and day. I've always liked the Sennheiser but to my surprize they sounded awful (no bass, piecing treble)against the cheaper Sony's.
You would have to pay substantially more to get even a marginal improvement in sound quality. The only area that perhaps needs more refinement is the treble which is not quite as sweet as it could be. I owned a website selling Sennheiser and Beyer headphones a couple of years back so I've had the opportunity to listen to many different headphones from £10 to over £200. The Sony's compare to headphones costing closer to £50 so a real bargain.
I simply can't stand ear piecing treble and tinny, thin sound which just ends up being fatiguing. Luckily the Sony's have none of this and instead offer a relaxed sound delivery with a meaty bass and full midrange. This does mean they are not as informative as higher end headphones but it is a good compromise. The MDRZX100B delivers with some short falls however at this price point it would be unfair to expect more!
They are comfortable, light weight, well made and sound superb. For £10 this is ridiculously good value for money. It's worth buying 2 just to have a spare, you never know when the price will go up.