Looking at another possibility for at least measurement of the captain's power on the tandem.
http://www.stagescycling.com/stagespower
According to the customer service people at Stages, it will go on a Shimano R601 crank. It would be turning backwards, becaue the off crank arm in this case would be the right not the left, but apparently that's not a problem.
I hadn't seriously considered the Stage's power meter before because of the early bad reviews. But it appears they've ironed out a lot of kinks.
http://www.dcrainmaker.com/2013/06/s...ew-update.html
I'm thinking of giving it a try. I'd like to upgrade our FSA Gossamer cranks anyway, and the price of the Stages power meter itself is relatively cheap by power meter standards.