FWIW, our tandem is an '82 Peugeot and for some silly reason I decided to keep it equipped with nearly all period-appropriate French components. Both derailleurs are Simplex, the front intended for a triple. (We are running 52/38/28 in front.) It is indeed floppy so early shifts are essential.

A challenge for me is to gauge the steepness and length of hill. Our middle-ring low is 38f/32r, low enough for us to power up a short steep rise with enough head start or up a shallower extended hill. But once I commit to that combination and we're partway up we had better not run out of gas. My sweetie always asks why not use the granny, and I have to reply that I misjudged it. We've learned that it doesn't like to drop onto the small ring under much power. So I usually shift the front early and liberally.

On the other hand, we have to coolest tandem on the roads! And the RD works quite well.