I'd only download it if it was free. The app store is full of junk like that.
They have a replaytv control widget for the PC/Mac but I never use it.
What I would like to see is a iPhone smart remote that, when you change to a channel, checks with the guide, the imdb movie database/wikipedia to tell you more about the show, director, actors, etc. Mine would also have an inflation calculator built-in. I'm always wondering if some pays $50k for an apartment in Manhattan in a 1962 film, what would that be in today's inflation adjusted dollars. But maybe that's just me. I can't watch tv without a on-line computer anymore.
Or maybe DVArchive-like capability on a iPhone remote control to download and view a movie from the replaytv to the iPhone for mobile viewing. I'd pay $0.99 for that.