So I’ve done two different TestFlight builds and I’ve fixed what I wanted to fix. First of all, the first TestFlight build was 360 mb or larger. Strangely enough I only found this out when I heard of the huge app size from my testers. Weird, since the app was just 50 mb on my phone and I didn’t add anything before I uploaded the TestFlight build. Turned out, it was due to the Deployment Target, which was set to iOS 8 (since I wanted to support iOS 8). But setting it to iOS 8 actually increased my app size more than 5 times of the original size. I’ve still no idea why this happens, so I’ve set it back to iOS 9. Too bad, but not a huge loss since iOS 9 is installed on 84% of all active devices and iOS 8 on 11%. But hey, I tried to include iOS 8 in the first place. But still, the good news is that the install size went from 360 mb to around 60 mb.
So that’s that. I’ve also added swipe gestures which improves the flow when using the app. Thanks for this recommendation Arthur, although you may never even read this. And I’ve added a How to use page, in case some user wants to know how things work.