Anyone who has spent hours in a caravan park kitchen, laundry or bathroom, knowing that if they leave for a second that their charging electronics will be stolen, think that the price for an on-bike charger would be cheap at twice the price for the convenience they offer.
I've never resented the money I spent on my E-werk and will happily upgrade when/if a better one is manufactured, irrespective of cost.
Definitely the best cycling accessory I've ever bought.