Help me understand Keys please

So i am a Fnatic Fan for a year now but only recently made an account and i want to buy merch now and participate more with the Community. I know Fnatic+ is a thing and i want to buy the jersey as well. Now i saw there was a system with Blockchain Keys once and i wanted to ask: Can i just buy an existing Key off somone on opensea. There are some for like 55 euros so that would be a lifelong Fnatic Plus membership with a free Jersey every year? Am i missing something, cuz this seems to good to be true?