Well it looks like it has been tried more than a few times. I think that I am a little confused here, physics wise.
I still can't get my head around why the single blade with counterweight would save weight. Doesn't the counterweight need to be the same mass as the opposite blade?
Wouldn't the extra lift from a 2nd blade allow you to make both of the blades smaller thereby saving weight???
I must be missing something major, otherwise why would they seriously try this?