1,000 times this, and this is why they are mired in an investor lawsuit.
This is just thinly-disguised lying. Ducted fans are more efficient than open propellers of the same diameter, which is a telling detail that they conveniently leave unstated. A ducted fan of 10 cm diameter cannot be compared with an open propeller of 4 m diameter, which is closer to what Lilium's competitors use. This doesn't by itself mean the ducted fan idea won't work, but it's ridiculous to imply that the ducted fan is somehow "more efficient" without talking about the propellers' respective diameters.
Why? Their point is that it's misleading to use data from open propellers and apply it to a ducted fan design. I would certainly hope that the critics tried to scale according to the diameter of the rotors. That is, they should at least assume something like a 10cm open rotor. But then it'd still be misleading to use data based on open propellers. Their point is that there are aspects of their design that increases efficiency that must be taken into account, and that's true as far as I can tell.
And why do you assume that scaling down the size of the rotor would make it less efficient, rather than more? I mean yes, if that's the only thing you do, it probably would be. But they're also changing the whole design of the aircraft specifically for distributed propulsion.
NASA is already demonstrating with the Maxwell X-57 that moving to many smaller rotors is more efficient than 1-2 big rotors, since you get additional lift distributed over the wing allowing for a smaller wing with less drag. I think NASA knows what they're doing.