it's 400 watts peak, which is more than i've ever used to ride up a hill. and 35-37lb is a decent (light) weight for an ebike. those things aren't the issues.
i assume you're not considering the singlespeed - your contribution to the hill climbing is going to be sorta limited, unless you've got legs of steel and heart/lungs to match. the 7 speed version doesn't list what size the rear cassette is, you should ask about that. also find out if the assist levels can be controlled, or if it's just going to pump out 400w going up a big hill until the battery is toast.
very attractive/low price point, so many of the components may not be top notch, but it seems like a nicely considered bike and i wouldn't let the 250/400w rating deter you unless your goal is to go up hills FAST.