This looks very interesting, just expensive for all it is

[Globalti]

I saw a much more useful accessory in South Africa, it's a retractable tow cable that allows a stronger rider to help weaker riders up hills. Expensive though.

 

[ColinJ]

Our USE is still fine on the back of our tandem. Because mudguard, I guess.

I've got one on my mountain bike. I have never been a fan of muddy rides and often used a rear Crudguard anyway so it never got too much muck on it. It stills work properly. It doesn't have much travel, but it protected my back a few times when I hit unseen objects at speed.