The i-Brace is designed to reduce torsional rigidity (aka: twist) in the mid-section of the vehicle. It tackles that same ‘exhaust tunnel’ weakness as the TB Crossmember Brace, and is designed to be an improvement in strength & function over the factory stamped-steel piece.
TB Performance chassis braces were one of the first things I did my my Fiesta ST. Why? Because: 1) They're relatively inexpensive, 2) they're easy to install, and 3) they won't void your warranty (if you're worried about that sort of thing). If you're a new owner of a FiST, these allow you to get even more response & performance out of the already aggressive chassis WITHOUT putting any additional strain through the engine or drivetrain. And if you've had your FiST for a while, even better, because it's gonna spark-up the driving experience, tighten up response, and remind you of how rad your car actually is & why you bought it in the first place.
PLEASE refer to this TB install article we did a while back on my Fiesta ST. It has specific info of how each braces will improve different dynamics of the car: TB Chassis Bracing FIESTA ST
And BTW - if 'who you buy from' matters just as much as 'what you're buying'.... let it be known that Danny Check of TB, is one of the most solid dudes you'll ever find in this industry. He's born & raised near San Diego, totally down-to-earth, a helluva rock-climber, and super passionate about the daily-lifestyle side of car culture & ripping around in fun cars. He will not put a part into production if it does not improve the vehicle.