Has anyone tried any of the charge adapters to allow the iPhone/iPod to successfully charge on older docks using firewire charging ?

I want to use my iPhone as a satnav/iPod in my car with the Connects2 unit I've got hooking up to my Kenwood stereo. It works great but it doesn't charge using this cable. I'm not sure if using the head unit to control the music will still work with one of these adapters in place. Anyone got any experience of using them ?

Thanks