first: it's not fully free to play because it doesn't include MoP and is more like an extended trial and second: Come on, don't tell me this link even seems a little bit legit
First: It's a free Battlechest. The one regularly available for $10. It's not an "extended trial".
Second: It's legit, which you would have found out had you bothered to read any of the other posts in this 9 page long thread.