We had that bike. Plus one on the rear hub being a problem, plus its not quick release. When we broke an axle, we replaced it with a better hub.
Overall, the Bike was a very nice value. Unless it's in excellent condition, I would not say its worth $700.
However, given what you could buy new, and what else you may able to find used, if it fits and and is in good condition, $700 could be worth it to get you into a very useable tandem.
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You could fall off a cliff and die.
You could get lost and die.
You could hit a tree and die.
OR YOU COULD STAY HOME AND FALL OFF THE COUCH AND DIE.