Been tandeming 40+ years.
Our advice: buy the best you can afford.
Chris King headset, FSA c/f cranks, Topolino wheels, Shim der., barend shifters, Tektro (rear) and D/A (front) brakes.
Keep it simple; no fancy/faulty electronics, no discs. Tried 'em, not dependable.
Our present Zona tandem is our 5th one. It currently has 45,000 miles on it.
Pedal on!
Rudy and Kay/zonatandem