I don't know about the voice guidance in yards, but in the metric world it sounds correctly: "in three hundred metres turn left", "in one hundred metres enter the roundabout", etc.
I guess that goes hand in hand with other imperial sizes - e.g. screw head diameters measured in 16ths of an inch, screw lenghts measured in 8ths of an inch, etc. After all, if a 16mm screw is defined as 5/8", and people find that perfectly normal, then why not apply the same logic to road distances?
Even if the TSR weren't working, you should still see something on the instrument panel, namely the speed limit defined in the navigation map. Without TSR the speed limit from the navigation data appears on Sync's touch screen. With TSR it should appear on the instrument panel.
How do I know it's working? Firstly, it also displays other traffic signs besides speed limits (e.g. no overtaking), so whenever I see one of those I know the TSR works. Secondly, there are a couple of places on my way to work where the real speed limit, as defined by the traffic sign, is not the same as the one stored in Sync's map. Most of the times the speed limit displayed on the instrument panel changes as soon as I pass by the sign, but sometimes it doesn't, which proves that the new speed limit is not merely embedded in the map, but detected by the TSR.