I fly a lot and usually fly United. In my opinion, United does a solid job boarding because they put out signs for boarding groups. 1, 2, 3, 4 and 5. Not every airline does this. The issue is when people don't listen and stand in the way of the group that is supposed to board. It slows the process down. If people could follow basic directions it would make things easier. Since people can't follow basic directions, I don't expect this new process to speed things up. Aisle and Middle seats will stand in the way of the window people while board. Families will still want to board together. You can't leave a middle seat kid at the gate while window seat parent boards.
If you have a small bag but don't want to pay to check it, just bring it to the gate and United will check it for free at the gate.
I fly in and out of Newark a lot, and I try not to check bags unless I am going for more than a week. When you return to Newark the baggage process is very slow.
Last week I was in Europe and flew on a cheap European airline and they had 2 staircases to board, one at the front and one at the back of the plane. It was the smoothest and quickest boarding, except for the guy in row 5 that entered the back of the plane.