As it comes from the factory, the Bionx unit is designed to INCREASE SPEED ... not REDUCE EFFORT (see my posts under the Bionx Tourer).
A long term concern for most Bionx users is whether their knees will hold up under the stress of using the higher gears that the strain gauge needs to keep the motor engaged.
In my experience, consistent riding at level 2 drains the battery in about 25 miles.