There have to be rules where those taxis can start, land, in what direction, time frames and over which places in a city. You need some kind of air control and "traffic rules". Drivers need regulated training in simulators and there need to be emergency procedures.
I believe that in the first few years such things won't be allowed near towns and cities. There will be similar rules like flying drones [1], but a lot stricter.
And the time saved by such travel will probably decrease when the sky starts looking like in the 5th Element [2].
[1] https://uavcoach.com/drone-laws-in-switzerland/ [2] https://media.giphy.com/media/Bs2pZhpxf2168/giphy.gif
