We bought the first two of the original Cytronex bikes in 2008 and got on quite well with them. I posted on here very positively about these bikes (under a different name, chris_bike, that lapsed when I changed my email). The range was not what it might have been, but that is a consequence of the batteries being relatively small.
We also have one bike in the new setup. It was built on a Carbon Planet X frame so not much over 12 kg all in. It works ok, but the set-up is quite flakey. The hall sensor that detects movement in the cassette is easily knocked out of alignment, which cuts all power. The battery is still only 5Ahr, which is really too small for any ebike. And the set up is quite expensive.
In truth, I think Cytronex missed their market with this bike. It should have been launched 3-4 years ago (when it was "in development"). There are now bikes on the market with bigger batteries hidden in the down tube and considerably greater range (Orbea Gain, Focus, Willier, Bianchi and even Pinarello). The cheapest, especially if you search for a 2018 model, are cheaper than a Cytronex conversion and have a better range.
I think the day of the bottle battery conversion is now past. I've recently found their after sales service wanting too.
We have two C1s, one on our lightweight Comotion Macchiato (weighs 11.8kg without pedals) tandem in Florida and the other on a nondescript road bike in the UK. Initially, last year, I put a EU version (max15.5 mph) on the tandem on the advice of Cytronex for higher torque, but soon found that at our combined ages of 159, we could not stay with our cycling group which frequently exceeds 17 mph, so I bought the US version (max 20 mph) and put the EU version on the UK bike. Now we can stay with the gang at, when required, the lowest power setting . We have ridden over 2000 miles since last May and only once, in fact last week, has the speed sensor come out of alignment and that was my fault through parking the tandem against some bushes.
I have not yet had a chance to really test the solo bike in the UK, but will do so this summer.
I have found the pre- and post-sales support from Cytronex to be exceptional; they respond almost before I have finished writing (slight exaggeration!). Delivery to the USA was three days from date of order on both occasions!! Fitting the kit was a 30-minute job.
Yes, there are etandems out there, but to have one like ours, which already cost new $12,000, fitted with, say, Shimano STEPs, would cost upwards of $15,000. The Hawthorne is priced over $20,000! So paying about $1200 for a C1 conversion seems to me to be very cost-effective.
As for performance, we easily get 25 miles when using the lowest (50W) power setting almost constantly over flat Florida roads at an average of 15.5 mph, which we did yesterday and had 25% of charge left.
For comparison, we also have in the UK a Circe Helios STEPS Separable tandem with a 418Wh Shimano battery (C1 is 180Wh). This bike weighs over 25 kg vs the Comotion's approx 17 kg with C1 and pedals. Although I have not compared them directly, I think that the ranges are very similar, which points to the weight difference and better efficiency of the C1.
We are seriously considering buying a third C1 for a Trek tandem we keep in the UK as we are so happy with the ones we have, plus the outstanding Cytronex support.