You can download it (free using the redemption code) then just delete it, but later down the road, if you want to redownload it, it'll still be free in your Purchased list, so you don't need to keep it on the iPhone if you don't want to.
Probably won't ever play it, but it's temporarily free to download so why not. Put it right next to Flappy Bird and Angry Birds in the last page of my Games folder.