Another way of setting two nodes adjacent to each other to exactly the same setting is to use vertical snap. Select the node or nodes you want to adjust, hold the ctrl key down and drag up or down as required. As you approach the level of the previous node you'll see that highlight and the next node will snap to the previous one.
Note that if the selected nodes are at different levels the differences are maintained. To snap them all to the same level you need to do them individually.
You can also snap to the previous flat section using this method.