I own an older model of this mower, the EM4.1. I'm young and healthy, although not particularly fit, and find it easy to push up my large, steeply graded, and damp yard. Quite simply, I have the absolute worst yard in which to operate this mower and it does the job, not well, but not bad enough to warrant the harm to the environment or my pocket that would ensue by replacing the unit...
It chokes up easily on high or wet grass, keeping the blades sharp and raising the height helps whenever this happens. The mulching blade will drain the battery faster, and the bag, at least on my older unit, is much too small and difficult to attach. In my case, which may differ from this newer model, these flaws have made it necessary to use the side-chute. Finally, the mower sold here today has a 19" cutting width, which is a bit smaller than the average gas mower.
As for the good stuff: This is pretty green. I read some statistic, true or not, that a gas mower engine is so inefficient that a single tank of gas will do as much harm as driving over 300 miles in an SUV. Even if that isn't true, the electricity for a single cut, even if you need two batteries, is much less expensive than the gasoline you'd otherwise require. You'll never have to run out to buy gasoline again, but you will need to remember to put it on the charger 12-24 hours in advance (slightly annoying with one charger and two batteries!)