*UPDATE*
Our Helios has now had a frame transplant to fit one with the shimano STEPS motor. It is absolutely brilliant. As it was just a transplant, I don't have the Di2 gears, which takes a bit of learning how to convince the motor to help, because it doesn't automatically sense them. It works so well that I rode it solo to work for ride to work day (around 16 miles, each way, mostly country lanes). I have really been delighted with it, not just that it helps with the hills, but that it helps with the idea of hills, so I rode to the severn valley country park, which is over a rather large ridge from us voluntarily, rather than letting the hill scare me into driving there.
The next thing I would like is to have it made splittable which can be retro fitted, which would increase our ability to travel by train.