[Gregol]

PureOS is based on Debian by the way (even on the phone!). The phone is basically running Debian. So if everything they added to it is open source then their claim "fuilly open source" is of course valid. Privacy wise Debian by default is very good but I don't know about their modifications.

The problem I see is mostly that the phone is a rather low-mid end device for the price of a flagship.

Yes, debian is very good, but for desktop. I don't think so, their modifications will be good for smartphones.
Larger companies failed. Windows phone, blackberry OS and ubuntu mobile didn't succeed. In this case the user base is of key importance. Android and iOS has so many users, and hardly anyone imagines anything other than these two systems.

There is also the matter of habit. It would be hard for me to find myself on a system other than android.