Works great on the few things that support it, BUT
I got given one free (old type). But since it only has HDMI audio, it would be problematic to install in my home cinema system (SP/DIF only). So it was left in the box.
Recently I tried ultraviolet, (which seems like a brilliant idea), only to find that nothing I own will actually work with it in a way that is beneficial. (PS3 could use it in supposed SD, but it looks and sounds more like VHS to me).
It was easy to install the chromecast with sound just coming from the projector for testing.
Iplayer and youtube worked fine from an android tablet, android x86 laptop and chromium (after installing pepper flash).
So I tried the UV apps (blinkbox and flixster video, both of which play the movies locally, but I'm not going to seriously view movies on a £60 tablet). Neither would work with the Chromecast. Blinkbox didn't offer the buttons on the tablet, and on the Android x86 device the buttons were there, but nothing worked. Flixster just errored that none of the movies were available for streaming. On chromium they failed too.
The device is now unplugged and sitting on the shelf. Like UV is is a great idea, killed/hobbled by lack of interoperability.
HDMI only (which if that were the only issue, I would get around). No support for BlackBerry (which via bluetooth is my main audio player). No support for Firefox. App support so poor, it offers nothing over a PS3.