As a San Francisco resident, I don't really see any reason to use this. I have Lyft for when I just need to get somewhere, and it's cheaper and more desirable than riding a taxi (yes, even after the improvements "uber-izing" a taxi makes), and I have Uber for when a black car is more appropriate, and Uber SUV for when I need to transport more than just myself or myself and another person.
It seems like those three services fit the full spectrum of use cases. Maybe this is just a way to appease the taxi cartel temporarily, while they don't realize their service is becoming obsolete.