Looked at the site for the FSA same 1.6X overdrive as the Schlumpf speed drive, but..
Chainring is 28t, vs the use of a 110 spider , so 34t or larger rings are possible ..
and the Schlumpf can use any crankarm 1 from a tandem kit , to get the pedal, RH/LH, threads
thats the Rt, of the front crank , + the left off a standard single crank
(they of course come with a set of cranks, you have choices)
the FSA is cable operated, so you have another lever on the bars..
vs just tapping the center of the crank with your heel, one side or the other..
Schlumpf High Speed Drive is the inverse of my mountain drive 2.5 x overdrive .. 27t/67.5t !