Purchased a Koso speedo for my Honda Ruckus. Thought I was going to have to drill out parts of the front wheel assembly (with drum brakes, yuck) and put in magnets, install magnetic pickup, etc, for the new speedo but then stumbled across this. Just unscrew the old cable from the old speedo and screw it into this and it plugs right into the new Koso speedo wiring! Then you calculate your wheel circumference and set a number of points of contact and you're good to go.
The documentation for figuring out how to determine points of contact was lacking but after I installed it and calibrated it the MPH was half of the actual MPH (calibrated to GPS) so I just doubled the number of points and then it was very close (within 1 MPH). Bumped up the circumference value of my tire another 50mm to correct for the 1 MPH difference and it was spot-on. (FYI, for the stock Ruckus tire, it ended up being 12 pts/1450mm circumference)