Or you could try WW1 style and have the whole engine rotate…
Did you actually watch the video? It's not just a broken two blade prop, the short side has a huge weight and the hub is some sort of gimbal. They flew with it and a two bladed prop and although it didn't shake the airplane to pieces and tear the engine off they found the performance disappointing. On paper a single blade prop should be more efficient because it'd be traveling through undisturbed air but I think that assumes the airplane is already traveling fast enough to make that a possibility, this experiment was done with a Cub, an airplane that can barely get out of it's own way on the best day. The big thinkers involved in the Rare Bear had a similar idea about reducing the number of blades from four to three and replacing the existing blades with a design more optimized for the RPM and airspeeds the airplane was running when all of the levers were pushed forward. And it was awesome to witness, that airplane at 500 mph and 4200 hp at 100' off the ground shook not only your insides but also the ground you were standing on. But it also came at a price, these modifications set up unforeseen harmonics, pilots used to talk about being able to hear the airplane coming up to pass them from behind as they were balls out in whatever fighter they were racing, their airplane wasn't the only one getting a bit fatigued by this phenomenon. Had unlimited funds been available the problem could've been managed, but now it's forever retired, not because it was unreliable, inefficient or unsuccessful. It'll never come back because of some very stout legal agreements and a loss of knowledge. Some folks say there's more than one example and I can tell you unequivocally there was only one prop ever built and it'll never fly again.