Pros
* Probably much cheaper than a traditional helicopter - you don't need any complicated mechanical components like swash plates. * Increased redundancy would be much easier - you can wire up batteries in parallel, and it can no doubt fly with a significant number of broken propellers. The only other component is the microcontroller, which is cheap enough that you could have multiple copies of it. * Looks like you could fly it indoors fairly safely (in large buildings). With minor modifications it could be flown closer to buildings more safely than a traditional helicopter. * Easy to remote control, as already demonstrated in the video! This could make a great medical evacuation helicopter. * Should be virtually maintenance-free. The only thing I can think that you'd need to do is replace the battery.
Cons:
* Undoubtedly has a much shorter flight time than non-electric helicopters. * Lower capacity than (most) traditional helicopters. * Can't autogyro, so running out of fuel is much more serious! * Possibly costs more to run when you consider the cost of replacement batteries. Hard to say for sure.
It's certainly not a worthless design.