Nah, on bike you push yourself and 2 wheels, on a tandem you push half a tandem and one (probably slightly weightier) wheel. I reckon even if you're not quite as efficient as you are on one your own bike you'll still be quicker. The pedals will be synchronised to offset some of the problems of only concentrating on what you are doing yourself anyway, and you'll be on a tandem, so thinking about the other mandem.
Nah, on bike you push yourself and 2 wheels, on a tandem you push half a tandem and one (probably slightly weightier) wheel. I reckon even if you're not quite as efficient as you are on one your own bike you'll still be quicker. The pedals will be synchronised to offset some of the problems of only concentrating on what you are doing yourself anyway, and you'll be on a tandem, so thinking about the other mandem.