I've had my Helios for about a decade now.
Mine's got SRAM dual drive for the gearing, but they don't make those any more. Hub (or combo) gears are ace - makes shifting at the lights an option. I chose the SRAM because I wanted shorter cranks for both me and the stoker (smallest was about 6 when we got it, and with standard length cranks would probably have needed shorterners, and I'm a shortarse with cranky knees) and the dual drive had them as standard. I bought mine from Cycle Heaven in York, but I think Butterfly occasionally OTP got hers direct from the source, and then took it back for an electrification a few years later, and had only nice things to say about them.
It is, I think, the second most expensive thing I have ever bought, still one of my favourite things I have ever bought, and will be going to live with my small niblings soon so they can discover the joy of tandemming.