The item seems to have been removed.
On the whole these keys are generally dodgy and you are better avoiding.
For example when a large company buys Windows they dont get hundreds of Windows boxes and disks they just get one or two disks, and then a "key" that can be used many many times for everyone in the company.
It is these keys that can be stolen and sold.
While they may work at first, if Microsoft realise the key is NOT being uses on a computer owned by this company they will give yo ua warning (via a Windows message) and eventualy Windows will stop working.
This is just one example, another example may be a person selling the same key over and over again again Microsoft put a "stop" on it.
Generally avoid the dodgy key sellers.