A couple of points worth emphasizing. First, don't be thrown off by the redemption code -- it's not just for Joker, it gives you a $3 rental for any movie in Vudu's library. Also, you can rent any format, from SD to HD to UHD, and they're all $3. Since UHD movies at Vudu are usually $6, that means you can watch for half price.
If you've never rented from Vudu before, you'll need to create a free account before you redeem the code, and then any movies you browse will reflect the reduced rental cost. Personally, I will not be choosing Joker -- it might be an important, artistic film, but it looks aggressively unpleasant to watch. I might give Zombieland: Double Tap a spin, though. How will you use your $3 Vudu rental? Sound off in the comments.