Sorry for the question, but I honestly don't clearly understand this issue (well, not an issue at all). So, I modeled a simple door knob, with a considerable low topology because well, I didn't think I would need more, also, I've inspected some models with not-that-much geometry and they look smooth. But there is something that I'm clearly missing here, because the edges of the door knob looks way too hard. I've read on the site that it may be something about the normals? But pretty much all of them suggest to use Shift+E to apply an Edge Crease, which doesn't seem to make a difference.
This is my door knob. As you see, it looks like very low poly, instead of smooth. I should say that the door knob is part of a bigger model (a small wooden warehouse), and not a separate part on itself.
As an example, here's another door knob from a another model which it seems to have almost the same geometry, but this one looks smooth.