I was looking at the super street cage that Kenny Brown manufactures and am curious how much of an improvement the addition of one would make. What is required to install one, mainly how do you get it into the cab of the car? It looks like it comes already welded together, does it, or does it come in pieces? How much of an improvement will I experience compared to running my car with just sub-frame connectors?

The roll bar or cage will come in pieces. It needs to be welded into the car. Mounting plates need to be welded to the floor for the bars to attach to them. This will mean removing interior to access and weld. You can get swing out door bars to allow easier access in and out of the car however the back brace bar makes it very difficult for any access into the back seats.

Sub frame connectors just tie the front and rear subframes together to make a unibody car similar to a full frame car. Installing a roll bar or cage stiffens the entire chassis up to prevent body flex.

Even a real full frame car like a G-body will flex if there's no roll bar or cage.