I bought these wooden sides having already purchased a cell 90 case. These are pretty essential in that they will help prevent any dust from coming in through the sides into the case. They also improve the look of the case to no end. What does sting a little is the price for what is essentially two small bits of wood. Could be cheaper though this is obviously no fault of Thomann's.
These are very nice, great for a breakout skiff. Pennsylvanian cherry wood apparently. Lovely wood. The pilot holes are very difficult to screw straight into though, I had to drill mine out a little bit.