As the Mac Observer points out, the US$0.99 app doesn't allow mirroring or the streaming of any content with DRM, which means movies and TV shows purchased from the iTunes Store are out. It also doesn't support music streaming at this time, which could be a deterrent for some.
The developers said they are checking into the possibility of streaming music and admit in the version notes that there's a lot of work yet to come. But the reviews thus far say that the app is stable and works well. If you give it a try, let us know how it goes.