The concept of the “fan at each corner” flying car has cropped up repeatedly every few years since the 1950s. Typical designs involved belt drive from a single engine such that the loss of a single belt, let alone the engine would have been fatal!
The two things that have changed over the last decade that make the whole prospect more realistic are: Light weight high capacity batteries able to drive independently controlled electric motors; Enough portable computing power to provide computer controlled stability.
This latest concept is, I believe, able to handle the loss of two rotors even if they are on the same arm. That is interesting because I assume it means not only that the four rotors on two opposite arms are able to support the total weight, but also that the rotors on the third ‘good’ arm are able to rapidly switch between forward and reverse to offer the necessary balancing.
I think Piltdown Man does a good job of listing the other issues important issues though…
I'd also like be convinced that it will fly through windshear, turbulence, will miss-unexpected obstacles in its path, will divert if necessary, will have battery assurance programme, …
For me, 10 000 hours of operation without death or serious injury will the minimum for considering a flight in one.