Basic Trope: An apparently-decrepit vehicle turns out to be superior in performance to newer, shinier machines.
Straight: Ben's Mini-Mecha is dented and scarred with flaking paint, but its speed and power are visibly better than the other models shown.
Exaggerated: Ben's mecha is covered in rust and sloppy jury-rigged repairs, but it can outrun fighter jets while carrying entire freight cars.
Downplayed: Ben's mecha is less stylish than the others in the show, but it runs measurably faster.
The company Ben works for is running on a shoestring budget and can't afford nonessential repairs. They make up for it with ingenuity, and their clever designs are better than the standard.
The other mecha were all built by Honest John's Dealership, and were made to attract suckers by looking nice, since aesthetics are cheaper than quality. Meanwhile, Ben's machine looks rather weary after all its years of service, but still packs a punch because it was built to last.
Exploited: Barb bets on Ben in a duel, knowing that most of the people gambling will underestimate his odds.
Defied: Ben buffs, polishes, and paints his Mini-Mecha religiously.
Discussed: "The first lesson you will need to learn is a simple one: underestimate no-one. You see that heap out in the yard there? Ben, show them what it can do."
Conversed: "You know, I can't see why the mooks keep getting fooled by Ben's mecha. Every old model you see is better than the new ones."
Deconstructed: Ben's mecha is as fast as it is relative to the others because it was built right before new regulations banned the use of its core technology for environmental and safety reasons, and he ends up facing legal charges for continuing to operate it.
Reconstructed: Ben's mecha is as fast as it is relative to the others because it was a Super Prototype when it was built — which explains why the aesthetics ... aren't there.
Back to What a Piece of Junk, and don't let the rust fool you: that link's just as fast as anything out there.