Typically the economy chassis have less adjustability and cheaper components. Top of the line karts usually have billet pedals with very little play in the mounting pivots and are fully adjustable, they feature all magnesium components like hubs, sprocket carriers, bearing cassettes. And they usually have much better brakes and bearings, resulting in a chassis that is more free rolling and faster. All the latest enhancements and newest frame designs are used on the top of the line karts. The economy karts are usually an older frame design, have standard components with much less or no adjustability and are designed for entry level karters.
To echo what Walt said above, there is absolutely nothing wrong with these so-called economy chassis. They’re fast. You can win in them. They’re good karts.
It all depends on what you want to do. They might not be the ticket if you’re gonna do some big national/international race, but they are perfect for club racing where you’re racing for fun, experience, and laps. All without spending a lot of money.
Economy chassis can also be upgraded over time. You can pick up those fancy components and add them as your competition…and pocket book…dictates.
Again, it all comes down to what you want and need to go racing.