I just checked the app and the Theory 4 in 1 app doesn’t have a revision section. You can do full mock tests, or practice questions on specific sections e.g. alertness. But, when you practice questions you can click an explanation button, so it is possible to just learn from scratch by doing the questions and reading through the explanations. Theory is a fair bit of common sense—so I reckon if you only want to get one app, you would still probably be able to learn the theory although there isn’t a revision section per se. However the app does have revision and practice sections for road signs, and the Highway Code, as well as lots of hazard perception practice, all of which is super helpful.
On the the other hand, the DVSA Theory Test app (not the bundle, just the single app) does have a more detailed revision section, then has plenty of mock tests and practice questions. You also do get the Highway Code as an extra within the app, and 20 hazard perception clips, but not much on road signs (it has the theory of them, but the other app has pictures and explains in more detail) and 20 hazard perception clips, which isn’t many if you’re like me and struggle with practical driving more than learning theory.
Personally, I used the DVSA theory test app revision section to learn the content, then did mock tests on the DVSA theory test app and Theory 4 in 1 app. Then I did the 20 hazard perception clips in the DVSA theory test app, 30 clips from the DVSA hazard perception app (I got the DVSA bundle with the theory test, hazard perception and Highway Code apps), plus the 60+ hazard perception clips from the Theory 4 in 1 app.
As I’ve mentioned before, if you only want to get one app, there isn’t a huge amount of difference between the DVSA theory test app and the Theory 4 in 1 app. If you can memorise information fairly easily and have already had some driving lessons so know the basics, but struggle with hazard perception, get the Theory 4 in 1 app. If you have good road sense and practical driving skills but find it difficult memorising information and knowing all the small details and formalities, the DVSA app is probably better because of the revision section. If I’m completely honest, I would 100% recommend getting both the DVSA theory test app and the Theory 4 in 1 app - I’m aware this would be £9.99 but it’s cheaper than having to resit, and the two apps combined do have literally everything, and lots of practice stuff, so if you worked hard and fully utilised them both you’d stand a much higher chance of passing first time.
If you’re still unsure, I’d google hazard perception tips, read through them then search free hazard perception tests and have a go at a few. If you fail them and/or find them really difficult, and despite doing a few of them your marks don’t improve much, then maybe go for the Theory 4 in 1 app as this has a lot lot more clips so you can really practice and get used to it. If you’re fairly happy you could improve your score without much effort and don’t struggle too much with it then go for the DVSA app. The choice really is about whether you want the in depth revision section of the DVSA app, or lots of extra hazard perception clips from the Theory 4 in 1 app. But personally, if at all possible I do think getting the DVSA and the Theory 4 in 1 gives you the best of both worlds.
Feel free to reply/PM if you have other questions, otherwise good luck!