regarding couplers, we've had a Thorn tandem with couplers, and there is no way that I want another tandem without them, so it was a must have for our new Sapphire Pro, in fact it dictated that we bought a steel bike.
We used the couplers a lot to transport the tandem long distances inside a VW Golf estate car, also could bag it up (Ground Effect bags) and take it on Eurostar.
Yes, the couplers are expensive, but if you have an estate car, then you don't need a roof rack and the consequent poor fuel economy.