I love looking at the whole range of tools all designed to accomplish the same task. The least expensive get the job done, eventually. The top of the professional line get it done in the blink of an eye. How about hanging drywall?
Driving drywall screws is actually a complicated task. You need to hold the drywall firmly against the stud, because the softness of the drywall will not allow using the screw to pull it tight. Then you need to drive the screw just enough to create a dimple that can be completely covered with plaster, but not so deep as to break the paper.
So you could do it with a hand screw driver. Your arm would probably fall off before you finished a room, but we do often "adjust" screws by hand that were not properly driven with other equipment. Driving drywall screws with a regular screw gun is certainly faster than by hand, but it is extremely hard to stop at the right place.
You can buy a simple "dimpler" that attaches to any drill. Most dimplers are sold without the little magnet ring that goes inside. Don't try to use it without that ring. Why they sell it separately I don't know. The dimpler is the DIY way to drive drywall screws professionally. The magnet causes the screw to stay put so you can work with one hand on the drywall, the other holding the drill. You go full blast into the wall, and the collar on the dimpler disengages the drive when the screw is at the right depth, you don't even have to stop the drill. It works will, as long as you drive it straight into the wall so that the dimpler hits the drywall square. By the way, if your screw tip is getting warn, just pull it out with a pair of pliers and replace it with one of the same length. Dimplers last forever.
The professional drywall gun is a whole drill designed just for driving drywall screws. It is light weight because it doesn't need power. It has a magnetic head and built in clutch to control depth. This is the gun that the dimpler imitates.
The latest in professional screw guns is from Senco Tools. They have a battery operated drywall gun with a collated screw feed, making this thing work like a machine gun. Now you don't even have to dig into your pockets to find the screw. Of course one catch is that you have to buy your screw strips from Senco as well.
Another version of this is just the front end that is then attached to your own drill (only certain models fit). By the way, both of these guns can drive more than just drywall screws. They can work with Robertson flooring screws as well, even using extensions that allow you to not have to get down on the floor to drive screws into it.