Is it a deal? Yes, in two different ways. The movie costs $14.99 from competing services like Amazon Video, Google Play, and Vudu, but they only offer the movie in HD (1080p) quality. So, you’re getting a 4k movie for a third of the price of an HD movie.
Apple’s iTunes version does not feature HDR (with either Dolby Vision or HDR10) but the 2160p format effectively increases the resolution by 4-times that of Full HD.
Gone Girl was nominated for an Oscar “Best Performance by an Actress in a Leading Role – Rosamund Pike”. And, with a soundtrack by NIN’s Trent Reznor and composer Atticus Ross the movie is even great just to listen to.
And, don’t forget Apple is a Movies Anywhere partner so the purchase with iTunes will likely get the title showing up on other services (albeit in HD).