Thanks for your input!
I’ve finaly upgraded to FPOOS! We’ll see how it works but it should be easier to stay up to date…
FYI, I’ve installed FPOOS from my Android 5.1 rooted device using TWRP but not with Fastboot (as this method seems not to do a “clean install”). After that, I added the Google Play in order to install easily all further apps. Then i root the device by simply tap many times.
I hope my summary may help others as i found it difficult to understand the right way to do it s i could only find bits and pieces of information everywhere…
peace,
Nicolas