I think this sort of opinion is through fear/lack of understanding of technology.
Not criticising, and I am occasionally guilty of it, but a hidden physical punting phone has very little real difference to a hidden punting app. If you understand how to do it well that is.
Not criticising either, but that's simply not true. Apps go wrong, have bugs and security issues, get hacked. For an app like this to even work in the first place you have to assign it an awful lot of security permissions. There's no lack of understanding here.
I'm not comfortable having anything on my everyday phone that's related in any way to my punting activities. If you are, that's fine. It'll probably work okay, and you can call me paranoid while you happily use it for years on end. Personally I'll stick to keeping the two physically separate, and never having to worry that my phone might randomly do something disastrous when I least expect it.