I saved an image of my Win 7 system to a portable USB hd. I'm examining the contents now.
It created 11 folders (visible). I'm looking for any hidden files. I open a dos window. Run 'dir/a'. It displays everything including hidden items.
There are hidden folders and a hidden file called 'bootmgr'. These are easy to remove, if you know how to change file attributes.
In any case I think it is adequate if you perform a quick format rather than a long format.
Naturally, successful recovery depends on your having some alternate means to start up your laptop. This would be either from your recovery disk or some other disk (cd, dvd, etc.).
(I would like to test this hd in my Win 7 laptop, but it is usb. My laptop requires sata. Therefore I have no idea if this usb hd will really start up my laptop.)
Some people report they do not like Win 10. It's wise to leave yourself the option to fall back to Win 7.