Using an app is no different to using a laptop same security algorithms so yes I do know what I’m talking about
I think it's a personal thing like i said before. Your pc has only got that "reputable branded software" on it, because it's what you've chosen to put on it. Much the same as my phone has only "reputable branded apps" on it, because I have chosen to put those on it. if you secure your phone in the same way you do your PC, then give or take, your risk to exploits is more or less even.
I just checked the money saving expert premium bond calculator. I would have to put in about £17,000 to earn the same 'interest' as Atom at £10k. I'm going for the easy option.
Google Play is littered with insecure apps that you install without knowing on your phone. (eg. https://mobilemarketingmagazine.com/vast-majority-of-finance-mobile-apps-vulnerable-to-hackers) My PC has nothing but reputable branded software and proprietary Security software. Your phone might be more secure than the Bank of England, but no one I know has one that is anything close to secure. Take the risk if you want, it's a free country (allegedly)