I met a couple who rode a Bilenky at the GTR in 2005. Looked to me like a great bike for an 'occasional' stoker or someone with physical issue that made riding the standard bike design problematic. The separate gear selector for each rider would negate any cadence arguments.
But, the design does not lend itself to the advantages of a recumbent (less frontal area) or the advantages of an upright (light weight and ability to stand and climb).