Stranger things have worked but that does not make it a good idea.

I have to agree with Slowburn, at least to some extent. While the powerplant might in fact be efficient, putting the intake at the rear seems like a really weird thing to do. The video shows that the thing has a definite tendency to fly backward, and for pretty obvious reasons.
Maybe not such a bad idea, but at the very least I would put the intake(s) somewhere else.

85% efficient of what? I was expecting the rotors to be driven by the compressed air via jets at the tips at first, why else compress air etc. Looks cool so it's 90% there ;)

re; Craig Jennings
I agree blowing warm air through the blades and out nozzles at the tips would have provided the NOTAR performance with a single rotor and as a result fewer bearings and prevented blade icing as well.
I don't like the idea of loosing power to just one rotor either but that can happen with a gear driven system as well.

I agree the air intake(s) placement seems strange, why not, say, at the top of the fuselage where the rotor's downforce could help ( even if a tiny amount)? Even if at the front, with the airflow path under the cabin floor, at speed surely the increase of air pressure would "turbo" the efficiency?

Presumably the exhaust gasses exit through the slot around the saucer shaped rotor head possibly providing extra lift due to the Coandă effect?
Always liked the idea of coaxial rotor helicopters (not a new idea; Henry Bright patent 1859) lets hope it fares better than the Sikorsky X2.
Incidentally, if you blow air through the blades and out nozzles at the tips you get no torque reaction so you only need one set of rotors.
$200,000 makes it cheaper than a Robinson R22 ($260,000) so affordable as a trainer, although the CAA/FAA would probably have to create a "limited" licence specially for it.

I think it looks like a ducted fan gyrocopter.
I also think the compressed air should run the main rotor with 'jets' at the tips. It would - IMO - simplify the mechanicals of it.

Get a real scale model working before parading in Paris.
Seems they have described a direct drive, dual free-power-turbine, high bypass gas (low temperature) ?? engine...... but what is the powerplant driving the compressor..
Hard to see how they can reach even moderate efficiency (thermodynamically) given the small scale.
Um... High thermodynamic efficiency needs high temperatures the best they can ever hope for is to approach Carnot efficiency....
All I could find was this link: http://enzu.bruface.eu/media/filebook/files/Master%20Thesis%20proposal%20BruFacE%20EM%20engineering_Degrez.pdf
Mentions using a diesel engine for compressor power... and direct embedded turbines attached to each coax rotor...
Back in the old days they called the set-up a motor jet. 85% thermodynamic efficiency is Not likely given the most efficient combined cycle power plant is around 60% efficient.. Unless their gas generator is a solid oxide fuel cell.. and the compressor is electrically driven....
Also, don't forget that tailrotor helis also drift (sideways instead of backwards) Wouldn't a better bet be using electric drive at the hub, and whatever higher efficiency generator they can come up with (even batteries for short duration UAVs).

re; Pat Pending
The Sikorsky X2 was built as a proof of concept/technology demonstrator that fulfilled its design roll and was retired on schedule while also providing data for the development of higher capability production vehicles. How is that not faring well?

Is it me or is every claim they have made "in theory"?
They claim to have "proven the concept" yet they didn't. They built a scale model...that doesn't use the same technology....and have no working prototype.
Also, it can only lift 377lbs (in theory -ha!) ... two full grown men and some gear won't even get off the ground.
Verdict: Ridiculous, speculative, nonsense that will never see the light of the marketplace.