Have you tried using tha app on a device which is not the Stark smartphone? Does it work? Have you noticed any conflict with the interaction of the Stark phone with the motorcycle?
I guess that it should be usable provided the Varg phone is not running the app or, even better, if it's turned off.
This could be useful in case you forget or lose the Stark phone and especially for those people who have removed the phone cradle.
The only possilbe hazard that I see is that if your phone has been hacked someone can affect the behaviour of the bike, but I think it's an unlikely event.
I guess that it should be usable provided the Varg phone is not running the app or, even better, if it's turned off.
This could be useful in case you forget or lose the Stark phone and especially for those people who have removed the phone cradle.
The only possilbe hazard that I see is that if your phone has been hacked someone can affect the behaviour of the bike, but I think it's an unlikely event.