Being a typical engineer, I have to say "That's not how I would have done it!", but so what?
This electrically driven system is quiet, clean and economically cost efficient. A one-hour flight would cost something near to 6 Euro for electricity. In addition, the device holds few parts, which could wear out, making maintenance intervals and cost low and far between.6 euros is about $10, and if I drive my pickup for 1 hour at 60 mph at 20 mpg, the comparative cost of the fuel is currently pretty close. Keep in mind that we're comparing the cost of European electricity, which is expensive, to American gasoline, which in Republican administrations is relatively cheap.
Flight time is said to be 20-30 minutes which means I'd be falling out of the sky just as I get to work or back. Still, adding a small generator would extend this significantly.
The propeller arrangement leaves something to be desired as I'm having a hard time seeing this thing fitting in my front yard, never mind the garage. Still, I bet that an improved, i.e. more compact, arrangement wouldn't be too hard to come up with.
Oh yeah, I'm sure the motors are whisper quiet, but I guarantee the propellers will sound like a swarm of giant killer bees on crack.
Looks like fun, though.