"During flight mode, less than a tenth of the power is needed, dropping its energy consumption down to be comparable to that of an electric car."
There's this thing called glide ratio. It's the ratio between altitude and distance you can travel horizontally without power. Sailplanes get up to 1:60 these days, i.e., one kilometer of altitude gets you 60 kilometers of distance. That's with sailplanes that have a wingspan of 18 meters, and are designed for the purpose: low weight and optimum wing surface. Large aircraft have a glide ratio of 1:20 to 1:30, still with a pretty big wing area. Fighter aircraft are around 1:10.
The glide ratio defines your power needs. If this gizmo with its stubby wings and no laminar flow because there's fans all over the wing should even get 1:20, you still need to gain 15km of altitude to go 300km. Sure, you don't go 15km up all at once, and you gain some distance while in powered flight, but you catch my drift.
So you'll need enough juice to lift 500 kilos by about 10 kilometers. Oh wait, that is just the payload? The airframe plus engines is another 500 kilos, easily. Plus the batteries themselves. Good luck with that.
They should just glue on some solar panels. Problem solved!