The app will allow you to test the downstream and upstream speed both on mobile data (3G, HSPA, etc.) as well as Wi-Fi connections. It uses the same underlying speed test that you can use on our website, but has some additional features including a full graph of the speed profile to help you understand the results better.
We would stress that the app is still in beta testing, so any comments, bug reports and feature requests are welcome. We already have plans to add a number of features, but we need yout help to make sure the core functionality of the tester is accurate first :)
If you have any questions, please ask on our mobile speed test forum.