Black cab drivers have to study extremely hard..often for years to get a license and its not a cheap process !! They are scrupulously vetted over there past,ie..no one with a criminal record is likely to be taken on to train.Unlike mini cabs where it seems anyone can just become a driver in any old car..i personally would choose a black cab over a mini cab anyday...if for no other reason than safety. As for only taking cash..this is due to the cost of the card readers..