While it may be somewhat out of date, they do have several patents, which, by their very nature, reveal their "precious IP". If you look up the company name at the bottom of the web site, then go look for patents with that assignee name, there are only three hits (possibly more applications not yet issued, I didn't look). Now the patent describes what they were envisioning when the patent was written, and not necessarily what they wound up doing, but it would appear that they use a MEMS accelerometer and calculated acceleration (from the wheel sensor) to compute actual acceleration and tilt. They also use two air pressure sensors, one with a port facing forward and another to the side to measure wind speed (this isn't right, but the error could probably be calibrated out). The main remaining input is cadence, measured conventionally. Optional other measurements include altitude and temperature, which appear to be used either to improve accuracy in other measurements or to fine tune things. A roll-down calibration followed by a curve fit allows a measurement of rolling resistance and air resistance. Pretty much the rest is a matter of math.

To the original question, as far as I can tell, since there's no crank or pedal based pressure sensor, you can only get total power, so if you're looking for something tandem-specific, you're not really getting it here. You can compute the total power, but you can't separate captain from stoker. If that's what you're looking for.