Re: Not so easy
Really? I'm doing precisely that. I have Mint on one disk, Win10 (boo, hiss!) on another, and select them from the BIOS on boot (it defaults to Mint though).
I installed Mint from a USB pen drive after using of those live USB compiler thingymagubs that you point to the Mint iso and let it do its thing.
It wasn't what I'd call difficult to achieve by any means.