I use a GoPoint BT1 bluetooth unit when I track, it seems to work fine. It connects to my iPhone and gives throttle, RPM, speed and gear selection to Harry’s Lap Timer, Grand Prix Edition.
That said, once in a while I get errors with Harry’s. Harry’s is famous for this, so it may have nothing to do with the Viper. I think it’s because the GoPoint was loose, in fact it fell off during one session when my friend Mike was driving at Laguna Seca. Pretty sure he knocked it off with his leg, as I didn’t tell him to watch out for it when entering / exiting.