Unfortunately, Beamer can't stream DVDs (although it can stream the individual VOB files contained in a ripped DVD's VIDEO_TS folder). And Beamer converts multi-channel audio tracks to stereo, so you lose surround-sound effects. (The developer's FAQ says future versions of Beamer will support multi-channel audio.) Finally, the developer says that sometimes Beamer may have trouble streaming extremely large files, although I experienced no issues with ~1.5GB .m4v files streamed from a 2010 Mac mini. (I've seen a few reports of problems with files 4GB or larger.)
Beamer does only one thing, but in my testing does it well. And at $15, it's a lot cheaper than buying a new Mac just to get AirPlay capability.
Sign up for CIO Asia eNewsletters.