I've had the Nevo NuVinci for a little over a month. I'm not a prolific rider, but I've put a little over 100 miles on it (almost all of it on my 4-miles-each-way commute). In a word, I think the bike is fantastic. By way of background, I weigh 200 lbs and bought the larger frame with the Performance CX motor (20 mph top speed, 75 N•m of torque). The bike is built like a tank-- there's no flex of any sort that I can detect. The road to work is not in the best shape, lots of dimples, mini-potholes, uneven pavement, etc. I feel very secure going over it even at speed. There are a couple of downhill stretches where I've gotten it up to ~28 mph for several blocks and the thing is stable as can be. Additionally, I take my front wheel off every day at work (it's a Suntour quick release which, as far as I can tell, would require changing out the entire fork, etc. to change to a non-quick release) and it fits true every time I put it back on. No wobble or anything. The only minor gripe I have is that the front fender can scrape against the ground with the wheel removed-- I think mine has gotten very slightly misaligned as a result.
Things to watch out for: nothing, really. I bought it sight unseen, based on the video reviews here and at Citrus Cycles. In fact, I had never ridden any sort of electric bike before I received my bike, not even a test ride. It's a bit of an unusual sensation the first time you pedal with this thing as there's a very slight delay between your pedaling and the motor response. I notice it most at stop signs in Turbo mode when I start to pedal but have to stop for whatever reason, and the motor pulls me along for a split second before it cuts out. I don't think that' unique to this model, I'm sure every Bosch motor has the same issue. Anyway, it's really only noticeable in max assist-- anything less and it's not a problem. If you can stomach the cost, I highly recommend this bike. As best I can tell, it is one of the few bikes out there with: low-step frame; mid-drive motor; battery placed mid-frame. Those three were non-negotiable for me, which is how I came to this bike in the first place.
The one real consideration is how best to lock the bike. Because it's lacking a top tube, that eliminates a lot of options. Of course I use the built-in frame lock every time which should secure the rear wheel, and after a lot of time spent at thebestbikelock.com I decided I wanted the Kryptonite New York Fahgettaboudit Mini (link). However, with no top tube and a very thick down tube, the only place to use that lock is the seat tube. So that's one thing to keep in mind. The other issue is one I mentioned above, the difficult-to-replace quick release front wheel. You can bring it with you, and in fairness it is VERY easy to take off, but who wants to do that all the time? So I also picked up the Abus Bordo 6500 folding lock (link) that I use to lock the front wheel to the frame. With the battery removed, this lock will pass through the front wheel and the down tube; with the battery in place, it's not long enough so you have to fit the lock through the wheel and the gap between the head tube and the suspension fork. It's not the most elegant solution, but it works. In this way, you can secure your front & rear wheels and the bike itself. That's a lot of money to spend on locks, but as a percentage of the cost of the bike, not really.
If it seems like I dwelled on the locks, it's because that's the most important concern about this bike-- making sure I keep it in my possession! Everything else about it just works, and works beautifully. I'd be happy to answer any specific questions you might have.
why did you choose a low step model? Any regrets going with a low step bike?