I have the Spektrum telemetry system. I my opinion, its a little half baked. For the most part I like it, but I've completely given up on the Tachometer/Speedo. I do use the temp sensor and the voltage indicator. I also have the lap counter and I like that.

But the Telemetry reciever unit eats batteries and you need to undo 6 screws, two phillips and 4 allens, to change the battery. I actually just mounted the battery on the outside because its easier.

They deffinitely need to refine it. They also need a way to export the data over USB to a computer.