Not sure if that key you got is real or fake, I know there are a lot of fake ones on eBay as well for very cheap.
However, the link I sent you was posted on a really popular website and no one had a problem with it, so....
I did a little bit study, end up choose this one. Some others are phone activation, or KMS, etc. This one is just a key, use like a normal key does. I did think about if it can be a fake key, but I intentional upgrade my windows 10 pro to the latest insider version (which kill the AppleHFS support) before I enter the key (via the normal activation page). I don't have a good definition of "real key", but if it can work like a real key in a official latest insider Windows 10 which connected to the MS server. I think I can consider it is real.