Rans Enduro Sport, Hase Kettweisel Tandem, Merin Bear Valley beater bike
I don't think that it works so well for enthuiast-type riders because it forces you to sit almost vertically.
I had a customer rave about them so I bought a couple for my shop. I'd install one onto a customer's bike and let them try it out. I think letting them try it out was a mistake because nobody wanted to buy it afterward. When I closed my shop I threw them into a box with a bunch of other purchasing mistakes and another bike shop bought them.