Purchasing a Windows License Key from a Trusted Source

Greetings,

I am looking to buy a Windows key for my personal laptop, which currently has Linux pre-installed. I have found a site offering a 50% discount through a YouTuber, but I am unsure if the key is retail or OEM. Can you confirm if this site is reputable and if it is legal to purchase an OEM key for personal use? Will it be permissible to use an OEM key on my laptop for personal use?

It's important to note that Microsoft did not sell Windows 7 keys separately; they were part of a package including DVDs and keys. I have removed the link provided and please refrain from sharing it again, as Windows 7 is no longer sold by Microsoft and there are no reliable sources to purchase it from.