If the circuitry cant withstand the small capactive load of a volt meter then it sticks no chance of withstanding the static and noise around a car electrical system
Whilst I agree with what you are saying, don`t forget that the (poor quality mass produced p.o.s.) hand held TomTom was designed primarily for Hikers and Bikers, not for in car !! And is not as bulletproof as in car products

Whilst I agree the early ones were, the later generation ones are designed for car- hence the waterproof version for bikes.
As for poor quality, I've never had a problem with the one I have, as oppose to the epic failure of the in-car one to get me even close to where I want to go- even after the 3mins it takes to program it. I've tried virtually every external satnav on the market, and nothing comes close to the accuracy or speed-of-use of tomtom iiho, and the 3 different makes of in-car I've used have been utter tripe in comparison.
that said, I don't use it to get to the end of my road as a lot of people do, I can find most major towns & cities in the UK without even a map (been around a bit.....), I find it's biggest use is city centres.... hence the OP