Bontrager has a new version of the Node about to be released, the 1.1 and 1.2. It remains the cheapest, lightest stoker option for the Garmin equipped tandem, that will allow use of the Garmin ANT+ cadence/speed sensor, and avoid having to put redundant wheel magnet/sensor. With my Node 2, we find it doesn't pick up the cadence/speed signal as avidly as the Garmin, and neither are the controls as navigable. Maybe with the Node 1.2 & 2.2 there will be improvement.

Node 1.1 / Node 2.1