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).
Years ago test rode one of the early Counterpoints, both as pilot and as stoker.
As pilot, did not particularly like the riding position but it does let you whisper 'sweet nothings' into stoker's ear! As stoker, was surprised how much extra 'oomph' I could put into the pedals by pressing back hard into the seatback. It gives the stoker an unobstructed view of what's happening . . . which could be scary for some! Great for touring, as stoker can see better and also do camera/video stuff.
Was not impressed with the climbing/accelleration/agility ability but that was mainly due to the big knobby tires.
The German version (Pino/titanium) has weight down to 30 lbs! Have seen one, but not ridden it.
Again, another variation in the tandem world!
Pedal on TWOgether!
Rudy and Kay/zonatandem