READ the book, then only use the apps to test knowledge. If you don't score highly enough, re-read the book. The Highway Code isn't exactly War & Peace, two hours tops, cover to cover, but VERY boring. The official Hazard & Theory book is a bit bigger, but still do-able in 3-4 hours over a couple of evenings. Don't waste months clicking random answers in the hope of remembering come the test. My mates did this and all failed 1-4 times having wasted ages. I passed first time after 3 days prep.
For the hazard clips, practise it like a new Playstation game. When you 'get it' you're ready.