Although I always welcome everyone's information because I learn a lot from it, this is more about feel.
I started with the 2 pt brace on my '11 Fiesta SES then after getting my FiST, I have had all 3 front braces on it.
In fact I helped develop the 4 & 6 point and did a lot of testing.
Yes the Fiesta as built by Ford does not NEED any bracing however, I was always taught that the stiffer the chassis, the better.
If you just look at the mounting of the front A arms, you see that the front bolts are somewhat long and this allows some flex of the arms.
By adding a 2pt brace you can eliminate this flex.
The same is true of the lower sub-frame, it too is held in with long bolts and also allows some flex.
However, now the flex is in the complete suspension cradle and the 4 pt does help eliminate this some and it is better than just the 2 pt.
The best bet is the 6 pt brace, as it not only does all of the above but also ties the sub-frame to the body and eliminates almost all of the flex.
You CAN really feel the difference.
Personally I don't care what you do to your car but this is what I did to mine and I LIKE IT.
Dave