I had same thought, what is advantage of using Uber in Tokyo? Within what considered as metropolitan Tokyo (東京23区内) taxi is abundant and usually have no problem spotting and hailing taxi, all need to do is simply walk out to one of busy street and do not have to wait for long before spotting taxi. The driver not knowing the destination pretty much become thing of the past that now pretty much all taxi in Tokyo has GPS. What I can think of advantage of Uber is English speaking driver? Maybe Uber is targeting English speaking visitors who do not have good command of Japanese in Tokyo?