How do you feel about converting your life savings into bitcoins and putting it all on the phone?
Honestly? I don't really know, I guess i would not use the current app because it is not updated often, but i might build one myself and put it all... maybe
I was mainly attempting to stress that cold wallets are more useful when the stakes are high.
A modern phone OS will have plenty of extra weaknesses when compared with a security-focussed server/desktop OS. For phones, security (and transparency/openness) ranks far below concerns such as price, weight, size, spec., mass-appeal, ease-of-use, and being feature-rich. I'm reminded in particular of an incident where Android-users lost bitcoins, not due to any user or app-developer error, but because Android's SecureRandom function was flawed*.
If you do ever decide to manage serious amounts of money with your own phone app then please be mindful of these extra risks. Good luck!
*Note that this flaw was found because of Bitcoin. Bitcoin demands much greater security than most other information systems. Even a mobile banking app is less appealing to hackers given that profiting anonymously is more difficulty and bank transfers can be reversed.