What do you mean that their concept might not work at all? They have flown several iterations of their prototypes already but maybe you have something different in mind, e.g. doubts about the possibility to scale the concept up?
It’s all unmanned unfortunately. Still waiting for them to demo at least a dummy payload like Joby did a few months back.
Also, Joby, Ehang, and Volocopter are much further ahead in the sense they have done point to point or are building out the factory (same time last year Ehang got hit by being called a scam by Citron, however).
From what I read, rumor is the big issue is battery density which is holding Lilium from being viable. We shall see!
Also, Joby is most likely the one to look at to track the progress of this air taxi segment since they have just Spac’ed and their aircraft is the most conventional.
Here are videos of recent test flights:
https://www.youtube.com/watch?v=0idI3sJJKZw
https://www.youtube.com/watch?v=SqMEFdbuzQY
https://www.youtube.com/watch?v=jqvMXoVZfDw