I got this bike back in December. I love it. But of course, it has to fit your needs. It works perfectly for mine, but I could see it not meeting the needs of others. For me, I got it as a way to commute to and from work. To work, I use e-assist so that I don't get sweaty, and coming home, I don't use the assist at all. Since the bike is light, it's pretty much the same to use as a normal bike when not using any assist. For me, it's the perfect balance of features and price for my needs. If you put in a 350w motor, then you would need a bigger battery--making the bike heavier and more expensive. Single speed works fine with the e-assist, even on hills, which keeps the cost and weight down versus having a bike with gears. If you are OK with the electric motor "helping" you get around, then this bike would be great for you. If you want to be able to cruise around without pedaling at all, then this bike isn't for you.
Specifically about your question of the 250w motor on hills... this bike is pedal assist only. It does not have a throttle, so you always do have to give some effort (pedaling) for this bike to assist you. That said, on the highest level of e-assist (level 4) this bike does most of the work going uphill, as long as you are going 16mph or slower. Above 16mph (even on flat roads) the e-assist is noticeably less, but it's still pretty easy to cruise at 19-20mph.
E-assist works as an effort multiplier. It's designed to multiply your pedal effort. I forgot the exact number and I'm too lazy to look it up, but I *think* on the highest level it multiplies your effort by 3. Or in other words, you only have to use 1/3 the effort to go the same distance on this bike (on level 4) as you would on a non-electric bike. With that in mind, on a steeper hill, you do have to pedal harder than on a flat road or smaller incline, but still only give 1/3 the effort that you would on a non-electric bike.
If you have any other questions about this bike, I'm happy to answer.
