A chain drive would be more efficient than a friction drive, owing to tire deflection caused by the loading of the drive roller. As to the 30% figure, I feel this is an inflated number based on personal experiences with both drive systems. The biggest drawback to the friction drive is wet roads, which causes the roller to slip. On the other hand they are less expensive, much lighter and much quieter than chain drives.
I'm currently building another friction drive for my wife, she wants no part of a chain.