The client works fine from what I can tell. The settings display the storage space, free and used, let you limit the upload rate, add a proxy, or change auto start and update settings. If you have selected typical installation, you may want to add the root node to the client so that all of your files get synchronized. Here you see a list of all existing nodes and their local folder, and get options to add or delete nodes.
To change nodes or add nodes to the client, click on Syncs in the settings. Mega has confirmed to us via email that the client has not been created by them. While it still works fine, it is important to know as you may not want to run a third party sync client on your computer after all.
Update: Turns out that MegaSync is not an official client created by .nz after all. While I cannot say anything about the client for Apple's iOS operating system, the native client for Windows has just launched semi-officially (meaning there is no official word yet on the Mega blog that it is available). First to launch was the official Android application, with the promise that official Mega clients for iOS and Windows would follow in September. Mega launched as a web-only service initially, but has expanded its reach by launching applications for various operating systems. In fact, it did surpass established services such as Rapidshare on its way to the top, and while there are still some services out there that are more popular, Mediafire comes to mind for instance, it is on a good way to compete with those services on an eye-to-eye level. The file hosting service Mega has seen an incredible rise in popularity ever since it launched in the beginning of 2013.