"Zero emissions at point of use is in any case a plus."
Who cares, it's an overall increase, a MAJOR increase.
First, it's a pollution rate of 0% to the X% rate created by VTOL taxis. It's hard to subtract via addition.
Then the obvious... 100 mile range. At best, that's 50 miles from where ever the charging base is to the taxi fare then back to the charging base. So realistically, only fat rich CEO's will be using these in densely populated cities that have landing pads everywhere, or in other words for the USA, strictly the New York City metropolitan area. Of course there would be much less pollution if they would use any type of land vehicle and the elevator.
Then there's still the discussion about create landing pads and charging/personnel stations solely for VTOL taxis... This will all be environmentally horrible, and all for the fat rich CEO.