5th Anniversary GG Poker Tournament for free!?

Hey Guys, i got a Email today from GgPoker that there is a free Way to play the 150 $ Tournament 5th Anniversary 5M gtd. if i deposit 300$ in the next Time.

I dont really get it, is it really for free or do i have to play with the 300 dollar cash game or stuff?

I mean, i could easily withdraw the 300 $ after getting busted the Tournament?
Why should anyone then buy the normal 150$ buy in then?