I am currently building a made to measure step-through for a tall woman wanting some extra 'umph'. The conundrum is how to present and pitch the best option for her given what's currently on the market. I recently wrote an article for BikeBiz (Nov 2017 issue 142 page 44) and the essence of it reflects my sense that something is still being lost in translation.
After much consideration, I have chosen a system which is straight forward to add or remove - a handbuilt frame is built to last a few generations so I like to feel that if the frame was handed on to a new owner, it could be ridden traditionally. This means saying no to the mid-motor and the heavier conversion kits. Handcrafting steel cable covers was fiddly but the outcome should look good as these will be sprayed with the frame.
Another key factor is Ah or amp hour - the battery I have chosen is a 17Ah - perfect for longer days out. The charger is also a consideration as this has to be transported with the user when going for a touring holiday. You don't want to be carrying the equivalent of a house brick or small vice. The front wheel must be secure in the fork with anti-rotation tab washers as well as a captive washer for safety. The wheel nuts are subjected to a lot of motor vibration and should be checked regularly for tightness. Consider puncture protection - quick note here to say that the Schwalbe Marathon Plus is much more 'forgiving' now than it was when it first came onto the market. Glad to see that improvement.
Now waiting for the electric conversion companies to look more closely at the spokes and rim options for building the wheel as well as the rack options for carrying a pannier as well as housing the battery securely. What else...well with all that power, it shouldn't be too tricky to offer a lighting system and USB plug in. Jumping on board now is a good thing - I'm showing my support for cyclotricity.com - there is always room for improvements and the answers are just a discussion away.
Finally, check out www.atob.org.uk as they have an immense body of knowledge on the subject and their pocket size magazine is well worth the small subscription of £12 a year.