I use them on both return and drive chain on my cheapie homemade trike. In terms of simplicity, you can't get better. It means you have one less roller to worry about, and since your return chain runs very close to the drive chain, a bit more ground clearance. Disadvantages could be a tiny bit of noise but that is partially muffled by the tube. They are easy to buy, usually normal pvc tubing 10mm cost around a dollar per metre. You would need a chain breaker, and to straighten the tube, you hook it to a wall, clamp the bottom, and pore boiling water into the tube and leave to rest. The tube then settles straight, as the hot water reshapes it (as they usually come round).
The last advantage is cleanliness for the chain and you. It cleans off the guck that can build up on your chain. It also allows you to handle your trike or bike without getting chain marks on your skin or on your clothes. This is often very important, as in recumbents, the chain travels between your legs as it comes of the front. This means that without tubes the chain can bounce around and leave oil marks on your skin.