The app was approved by Microsoft tonight and is now listed in the Windows Store. We will be publishing a blog post soon with more information on the client. The quick summary is that (a) it is only a Tech Preview, (b) it is RDP-only, and (c) you need to have a fully verifiable View Connection Server certificate and tunnel server certificate (if Secure Tunnel is enabled) to use it. The last part is due to Microsoft's requirements for Windows Store apps.
I hope you all enjoy using the client and find it useful. We have spent a lot of time on it and look forward to improving it more in 2013.