[sj4nz]

You have to be more specific: Secure from what kind of threat? There are many threats ranging from service providers deciding to uninstall "unpopular" applications that threaten antiquated revenue models to State threats used against activists and dissidents.

[MBCook]

I assume he means "threats that would allow another app or actor to read your private key".

[Retric]

And ignores the threat of a stolen device.

[pbreit]

Unlike most stolen PCs, a stolen phone can be locked or erased remotely.