If you're really interested in the best possible sound quality and noise isolation for £300, I'd advise you to forget about ANC headphones altogether and opt for a pair of wired earphones instead. If you spend the same amount of money you'll get much better sound quality than this.
Seamless Bluetooth pairing; Long-lasting battery life; Excellent build quality
Noise cancellation isn't as effective as the QuietComfort 35's; Sound quality could be better; for the price