How efficient is string bike? Is this really a revolutionary bike? Bicycles are getting evolved with good technologies or methodologies as the period changes. Now, this one bike, so called string bike has been introduced, which doesn't have chain, derailleur but gears (the website claims so). How efficient this bike will be when compared to the chained ones? Is this one really going to be a game changer? If not, what are all the disadvantages it has?

(this animation says how it works)
The general idea of "lever drive," or a reciprocating pedal motion instead of a rotary pedal motion precedes even the invention of the modern diamond-frame bicycle--consider the Special Star from 1886. More recently, there was the Facet Biocam,  the Alenax, and the Wall Walker.

Within the world of reciprocating drivetrains, the String Bike is interesting in its use of materials (dyneema to transmit power) and the ability to vary mechanical advantage on the lever arm (although the Alenax was able to achieve this simply using hub gears).

But check out what Jobst Brandt had to say about the Alenax. His basic point is that you're converting reciprocating motion to rotary motion, which is mechanically less efficient. I haven't been able to find any studies of the biomechanics of lever-drive bikes.