I want to flash indeed, for the nexus 5 hammerhead. I want to better understand UT and the process of installing, that's why I like doing things myself. And Ubports needs to download many files when installing, then it would save me time to manually flash UT since I already have the files (images), especially if I want to do the operation several times or on several devices (considering that Ubports is installed on another PC or the cache is cleaned for some reason).
I also like being able to do the stuff without internet connection.
But there is a risk of getting the device bricked, that's why I need to be sure first.