The key worked! After payment confirmation it took about 20 minutes, as impatient as I am. I contacted them on Facebook when I didn't receive is after 10-15 minutes. They immediately responded there and I received the email with the key. Thanks, It looks sketchy I admit, but I recommend to all!

Clean install of windows 10. Works perfectly!

Worked perfectly! My clean windows 10 pro activated in one click!

Got key after 10 minutes and works perfectly, thanks!

Used it for clean installation - no issues. After upgrading motherboard and CPU, I wasn't able to reactivate, so I bought another one. It seems you can use this key directly without doing a clean installation, if Windows version installed matches.

Note: After motherboard change, there were two devices in Microsoft Account digital licences and phone support told me to delete the old one. Spoiler alert: That make things worse.