I Think it's a good plan...little bit more work but safer.
I want to try out win10. I don't want the upgrade to contaminate my perfectly running win7 pro. My plan is to cone the win7 HD to a new HD. Take the present HD out of the laptop and install the cloned one. Then upgrade to win10 pro on the cloned HD. If after a while, I don't like it, I would remove the cloned HD (win10 upgrade) and reinstall the win7 HD back in the laptop and keep running win7.
Does anyone see any problems with this?