Audi warranty re tracker devices

[Yarand]

My (Mythos Black / Express Red electric seats) TTS (built 25 Jan 2016, BW4) finally reached Sheerness from Emden on Friday evening and, my dealer tells me, will be with them tomorrow for collection Sun 6 March. Exciting! Getting Tracker Locate installed, although Audi dealer warned me that any issues with electrical faults caused by a non-Cobra device would invalidate the Audi warranty - they wanted to charge me £500 to supply and fit and guarantee a Cobra device, which doesn't even enable web tracking access.