As a previous owner of Bike Friday tandem, I’d have serious reservations about riding one your 6 foot tall son, particularly if he weighs very much. If he’s a big kid, and if you’re not well in synch with each other, the BF could be very uncomfortable.
I rode ours with our 8 year old daughter, and as a travel tandem with my 5’8” 125 lb wife.
Even at her relatively light weight, the bike was uncomfortably flexible, to the point she pretty much ended up refusing to ride it.
Admittedly, we were asking a lot of the bike doing hard rides, and fast descents. (50 mph plus was an adventure.) So it may work for you for casual rides, but I definitely test ride it first.
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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.