Just to let you know that I changed my mind about this kind of app after reading this document (in french), showing many security problems inherent to any app like this:

https://risques-tracage.fr/docs/risques-tracage.pdf

Thank's a lot for the answer and for your work!

Concerning purism, I think they go beyond what I expect in terms of freedom. This post shows it:

https://puri.sm/posts/librem5-solving-the-first-fsf-ryf-hurdle/

Not sure why replicant guys are mad. But on a fully free software phone I would definitely not like replicant, I want a real Gnu/Linux! Also they are reproaching Intel's management engine in purism's laptop, saying it would be impossible to disable, but they actually succeed in disabling it:

https://puri.sm/posts/purism-librem-laptops-completely-disable-intel-management-engine/

I recently learned about this project which seems very interesting, and allows clear control about non-free software and firmware installed. Could be usefull for a web consultation device on N900 or Sony Xperia Z2:

http://postmarketos.org/
https://wiki.postmarketos.org/wiki/Devices

I don't know if unity/ubuntu touch could be ported on it at some point.