We have the original c/f adjustable stoker stem that Bob Davis developed back in 2003.
40,000 miles later, it still works great.
We do have a ti 'glue-on' on it to hang our mini-garage door opener and put on a QR instead of a bolt so we can easily adjust the length of the adjustable stem when another stoker wants a ride. Have had to adjust it only a couple a times a couple millimeters at stoker's request.
We also utilize the c/f stoker hand rests that Bob made for us when he built the bike.
Pedal on TWOgether!
Rudy and Kay/zonatandem