It's not invisible metal..... you can see it.
Look onto windscreen from outside; there is a thin conductive metal layer in the windscreen that gives it a noticeable tint. How do you think electric current could otherwise flow through it (which heats it)?
This does absorb some signal - not only GPS but also other electromagnetic spectra. Hence VW have bundled it with the advanced telephone system.
VW are the first to use this wirefree technology to heat screens iirc, but it has been around for a while. My brother's mid-2000 C4 had a 'climate' windscreen (not heated) that took out IR to stop interior from heating up (or at least less) and that was pretty good at lowering the signal so it would take his handheld sat nav ages to get a lock and frequently drop out.
Ford's system has some more blank space in between the heating wires, so potentially this might allow more signal in. I never tried a handheld sat nav in a Ford though.
As I said, usually GPS (or GLONASS, BeiDou, Galileo) reception should still be OK unless the weather is poor (very overcast, thunderstorms, etc) or you drive in a location with tall structures (skycrapers, industrial plants, mountains, etc).
Right, so you claim the super thin layer of metal impedes signal and I quote "cripples signal".
1. If true, why isnt my signal blocked completely virtually all the time considering the rest of the car (other than the remaining windows) is a huge metal cage with much thicker metal walls than the glass.
2. If the glass is impeding signal, why does my Garmin GPS Forerunner and Edge (which use GPS and GLONOSS) devices also suffer location issues when in a heavily urban area or when I'm out in bad weather, which neither have any metal surrounding them.
It's a bit far fetched to claim a thin layer of metal has any noticeable effect on any signal in an already metal vehicle.