CREATING CUSTOM IMAGES

HI!

I just want to ask about creating custom image of windows 10 and windows 8, because I bought 8 Dell laptops which is all are same model and same specs and same drivers. I created a windows 10 pro custom images and installed to my laptops. every laptop has a embedded product key and when I checked all the product key my custom image automatically detected the product key inside and it matched on the system so I don't need to change or to buy any product key of windows 10 pro. some of my friends told me that its illegal because I am breaking the EULA, I told him the how do I break that every thing that I checked are perfect and detect the product key embedded and it matched on the OS that I loaded, he told me I copied the hardware info inside. I ask him how do I copy the hardware info if all my laptops has a same model and specs and drivers and I check the Generalize to make the computer unique information inside of it. 

please help me if I did the wrong way because I am so confused what he said.

thank you so much