This doesn't seem to be QoS in the sense used in networking standards: it's doing local "traffic shaping", giving priority to VOIP traffic versus other traffic. I can see it making a difference to people who are always uploading/downloading stuff e.g. Torrent users, but if I used VOIP, I would just be careful with what I was doing when making a call. But yes, you're still at the mercy of the state of the Internet: one swamped router on the way, the call will suck.
