I rented a KTM Racer mountain bike with a Bionx electronic battery this weekend.

I was absolutely thrilled with it. Hills have never been so inviting and I still was able to get a lot of physical fitness out of it.

Positives:
- Going uphill is a dream
- Going on dirt trails is absolutely no problem
- You decide how much battery you want to use. There are 4 "gears" with 1 being on low battery and 4 on high. You can use it without a battery too.
- Does recharge a bit when braking or when setting the battery to recharge as you go downhill

Negatives
- Won't go faster than 25 km when the motor is on
- Takes 6 hours to recharge
- Is limited in kilometers. The more battery you use, the faster it runs down
- Very heavy bike

Cost:
About SFr. 3,500 for bike and bionX.
For bionX and mounting: about SFr. 2,600 (without the bike)

__________________
Faith isn't about everything turning out okay. Faith is about being okay no matter how things turn out.

Good, more people falling into e-bikes
However, both KTM and Bionx are not ideal.

* expensive
* closed system (you can only buy battery/motor from Bionx)
* hub design -> no gears for the motor -> not efficient -> low battery range

Thus, I build a custom one for my wife.
Budget was ca. 1500chf (including the second-hand bike bought locally + good fork + disk brakes upgrade).
She can now do 30-35kmh on the street, keeping me on a road bike in a good shape. And you have to see those lycra cyclists being overtaking by a lady on a MTB