Thanks for your comments, Ludo. It's obvious people approach crosswords, especially themed crosswords, in different ways. You're obviously quite happy with how you tackle them - so that's right for you.
You knew enough about the subjects (in the puzzles I mentioned) to get so far … but not to the end. Other solvers knew enough about music to get the 'Stuck In The Middle' puzzle done, yet you seemed to feel that one was unfair.
Using only Chambers would mean that I wouldn't get many crosswords finished. You might think 'so what?', but I'm happy to learn new things, explore avenues I'd never considered - all the Red Baron stuff, for example. My son occasionally does crosswords - I don't think that he's expected to know characters from 'Blake's Seven', a series that ended before he was even born! (And it's definitely not a cornerstone of British culture, it barely registered on many people's consciousness.)