Just got my bumper in the mail - nice xmas present to get it to me so soon btw!
I have to say that it is really low profiled and barely added any size to the N4. I don't have the OEM bumper to compare to, but it does look smaller via the pics I;ve seen. Considering that, it probably doesn't provide as much protection as a sacrifice for the sleek dimensions. The fit isn't as tight as could be, but seems to fit just fine without any slack. Buttons are much easier to press than the cover I had on it just before, the S-Line TPU Gel Case. I like it.
I also have the Nilikin case that has nothing covering the buttons, and I would say the bumper is bigger around the edges of course, but the buttons are easier to manage with the bumper. The bumper also provides way better anti-slip properties front and back with it's more rubberized edges.
FOr now, I will roll with the bumper and see how it goes. I like being about to show off the back of the phone as my personal bling. lol