>>17135833Short answer: You don't really need it.
Longer answer: In most games where you're stuck with Federation MS, you're probably going to be using either the GM II, Marasai, Nemo, or some variant of the Rick Dias for the events of Zeta and Double Zeta. During the endgame against Char, the GM III becomes available at 26 tech and the Jegan becomes available at 28 tech. Your best bet is to try and rush the Jegan if you can, because the Jegan is good enough to handle anything the game has left to throw at you by that point. Compared to the Gustav Karl, it is almost as powerful and can be built in half the time.
>>17135860The Karl Gustav has 3 MS per unit produced. It is a far better mass production machine than the Nu Gundam.