Is this a Reliable site

Doesn't necessarily have to be "illegit"
I don't know Microsoft's policy concerning large enterprise customers and resellers. Could be they get a bunch of free licences along with the higher priced products (SQL, office complete, and so on) or that they buy stock of bankrupt assets and resell them cheap so they get your attention (and might sell you higher priced products)

But I agree, while the shop doesn't look too fishy, the price seems too good to be true.
 


Iv'e installed their keys on multiple pc's only once was I given a key that had been previously installed I was given a replacement within minutes and all is well.