Complex sentence: The advantage of CODOG is a simpler gearing compared to CODAG but it needs more powerful (or more) gas turbines for the same maximum power output and also the fuel consumption at high speed is even worse compared to CODAG.
Split into simpler sentences: The advantage of CODOG is a simpler gearing compared to CODAG but it needs either more powerful or additional gas turbines to achieve the same maximum power output. The disadvantage of CODOG is that the fuel consumption at high speed is poor compared to CODAG.