I have a Mirracyle on my winter bike, mounted conventionally on a flat bar bike: first bar up, second bar left--so yes, the bike is a bit wider. However I just fold that last arm forward to ride through my narrow back gate or to walk it through stairways or doors.

I find mirrors more important in winter cycling than at any other time. Even if I was as young as flexible as I once was, I can't do a full neck turn wearing a balaclava and face shield easily. And with the winter variations in shoulder/paint-stripe-separated bike lane conditions, you sometimes need to move left and take the lane more often than in summer.