Yes. But clients will understand this one better, with different known devices right in front of their eyes. Some of our clients can't map a resized browser window to a smartphone <-> tablet switch.
I agree. Just pointing out that it's not doing anything to emulate any of the behaviour of any device. It's still rendering as whatever your browser will show for those sizes, same user-agent/css/javascript behaviour. Still, as a demonstration tool it will be very useful.