I've tried a few of these visor kits, most have been complete pants at motorway speeds. The Supertooth Visor Lite works perfectly at all speeds. I have not had one person on the other end of the line complain they cannot hear me and I must have used it for 100 calls.
If you like gimmicks, this one is not for you. It has no text to speech, no auto off, all it does is answer calls - which is what I bought it for!
It has a volume switch, one button to connect calls & one to disconnect calls. Push the microphone to switch it on/off.
Very clever magnetic mount, which means when you need to use your sun visor, you pull the unit off one side & stick it back to the other - without taking your eyes off the road.
The only thing better than this would be a hard wired kit.