Hi John...
Echoing what others have said - you can bypass the w11 checks - but you may still be able to activate w10 using your 8.1 key. This is officially unsupported, but seemed to work the last time i had to rebuild due to an SSD crash.
(its worth creating a mirror backup if you want to try risk free)
I wouldn't touch the "cheap" keys....not when a legit w11 from the MS website costs AUD$249 at the moment...something smells waaaay too fishy...
here's some food for thought...
https://www.makeuseof.com/risks-usin...tivation-keys/