I thought about buying one, just traded my M35 and gave up on the idea. I doubt it won't work, actually I think it should work fine if not great. I've seen guys modding TPs and even a single stranded wire outside the noisy RF case improved, GPS and WI-FI signals, so apparently, even bare wire works sometimes. It should work better than something enclosed, say, behind the rear glass with metallic tint and/or embbeded FM power antennas.
If you're willing to drill a hole in your car, and you can't find a spot on your dash behind plastic or whatever, go for it. On my FX (see signature) I actually mounted my garmin GPS puck in the plastic where the wipers rest, very steatlh and work great there, but you have to route the usb cable through the firewall.