That's very location specific, living in London Uber is no cheaper than minicabs on most journeys, you already could find out the price of a journey beforehand, larger minicab companies already had apps for booking (albeit not as polished), and Uber drivers generally seem to lack the kind of local knowledge of roads that allow local cab drivers to choose faster routes than whatever route their app indicates.

The only area Uber has a compelling advantage is journeys of ten miles or more across the city, where not having to return to the area where the journey begun means that they are cheaper than a minicab.