That's a safety feature as much as it is an efficiency feature, it allows you to safely furl the blades when you are overspeeding, you can't rely on anything that isn't directly connected to the rotor base because it might be jammed, damaged, out of power or missing entirely. The blades governing themselves is the ideal, the linkage is there for synchronization and balance purposes only.
Probably wasn't clear above, I'm saying they weren't using a swashplate (most helicopters) they were using this little tiny tab attached to the rotor that could be controlled.
There are some helicopter blades that have this same idea, a little moving thing to control the pitch of the rotor over a swash plate