Sidestep was new to me so I put it to the test. I will post the tests at dougoffen.com/compare/02.htm

Basically sidestep said the lowest airfare for 2 from Toronto Canada to London England was $1008 including taxes and fees through orbitz. My site, using the exact same details found a price of $849.90. All details were entered the same and all flights turned out to be exactly same.

I think sidestep is not a slam dunk best deal. Now I only tested one senario, but a price almost triple is not the best price. Any travel agent will also double check actual availability, stop overs, insurance etc.