Based on my experience, it seems the Win10 readiness tool only checks for CPU speed, memory, and free storage space. Every machine on which I ran the analyzer has told me it's compatible with Windows10, only to find out after the update, half the hardware on the machine doesn't work.
Oh, and the tool never tells you when programs are incompatible with Win10. I had a system where 11 applications were automatically uninstalled from the machine, with no prior warning, and I was informed that they were removed only after the OS upgrade had fully completed. Thanks for the heads-up, MS.
Thankfully, all these systems were owned by other people who wanted me to update them to Win10. I wouldn't dare do it to my own workstation, or even my gaming rig.