I am somewhat of a newbie so take this with a grain of salt.

For starters if you install the optional steering arm you will probably want to also order 6mm ball studs. The 8mm ball studs that you are probably running currently may stick out the top of the arm and rub on the chassis.

The two positions on the optional steering arm will change the ackermann. You can read about ackermann if you Google it. In a nutshell, if you connect your turnbuckles to the rear most setting you will have less steering and if you connect to the front you will have more steering. This truck already has a lot of steering. I have not tested the optional steering arm, just installed it last night, but I am guessing the rear most setting will be preferred by most. I also believe that's how the FT manual shows it as their "default" configuration. It will ultimately be personal preference and based on the track layout you are running.

Now the experts on this thread can correct me if I provided any mis-information.