When charged and discharged the cells change their internal structure, expanding and stretching a little. The cells also change their shape due to the temperature expansion of the materials and the changes of the atmospheric pressure.
All of these factors cause that the cells are more or less blowing (inflating) and deflating. When the cells are closely tightened together one by one, this charge of shape (or size) creates a tension. That is why it is necessary to allow for the change of space and slight movement of the cell terminals. The original terminal connectors have a bulging U-shape that allows for the change of space between the connectors of the cells.
GWL/Team strongly recommends using these original cooper connectors. I you use massive single size buss-bars, such type is not flexible at all. There will be a pressure in between the crews of the terminals. In extreme cases this may cause cracking of the plastic material around the terminals and it may increase of aging of the cells.
Summary: it not recommended to use the massive buss bars. Use only the original quality copper terminals.