I am sure they made thing petrol proof and now on your BMW insurance policy .. your regular garmin won't be covered but only this one will be covered if lost/stolen.
Think about all the people working in that nice office in Munich and Bracknell to think up the idea of rebadging an existing product .. take value out of it and then charge more for it. That must have taken a couple of meetings and several management layers to sign that off! That's many many man hours that has to be paid for.