There is one of these (the little one) at Danbury Airport. I heard it run once. I couldn't hear anything else for three days. It was the same problem with the British Gyrodyne, too damned loud, and not really efficient. The heat source on the blade tips would make it far easier for a missile to lock onto and the noise, which was bad enough on those old birds, was beyond acceptable. I also suspect that driving the blades at the tips, which produces no torque reaction, a good thing, coupled to an engine which produces great torque created vibration problems. The ultimate ability to lift more lies with the blades themselves, not how fast you spin them, as the tips can never reach supersonic, or lift turns into turbulence, so there was no gain, just weight added to a helicopter that on a very hot day couldn't lift that much anyways. The noise though, those things were so loud.