Unless they have improved significantly, The voice commands have been next to useless every time i have tried to use them. They don't understand basic commands. (For Clarity, I have not tested them since about Feb, as i just could not be bothered as they where slow, wrong and frustrating. So they may have improved)
They work pretty much 100% for me (even with my British accent in the US), and yes they have improved since they first appeared. You might want to give them a try YMMV.