Hand held devices are not designed into a vehicle and are not sold by the vehicle mfr, therefore it is unlikely that Garmin could be held liable for a vehicle accident. Auto mfrs, OTOH, are extremely vulnerable thanks to stupid juries that blame the big companies and require absolutely no personal responsibility.
Voice controls work fine. The only restriction is that you can't enter a new destination which requires typing the address, looking at a list, etc - not things you want to do while driving. You can choose a pre-entered destination.