Both seem to have the same size (medium) although the Santana could be a large, difficult to say from the photos. I would say that frame quality is equal for both. They are steel frames but the Burley could be lighter because of the age difference; total tandem weight is probably around 40 lbs for the Santana and less than 35 lbs for the Burley.

Granted they fit you and your stoker the Burley seems to be a much better deal. Upgrading the Santana to 9 speed will cost you a new wheelset, a new cassette, and new brifters.

Prices are fine for both but at $800, and may be less, the Burley is a 'GO FOR IT' deal.