This seemed a good deal - these have been around a while now but the gold versions are usually dearer so £11.99 is a good price. There is free postage and I think currently a generous 15% cashback via quidco bringing it down to £10.20. Not sure if this version is as good as the official M-Cube but worth a punt I think.
Golden Ballz (or the Wiki M-cube) is a stack of 216 magnetic balls fashioned into a cube that you can pull to pieces and create infinite patterns with. Make them into a long string, fold them into shapes, or try and make them back into a cube again - all are possible (and infuriatingly difficult to complete). With one of these on your desk or in your pocket you’ll never be bored again.