How do the side slit bangers work? What are the benefits compared to a regular quartz banger? Why do some newer bangers have slits on the side?

They work the same as a normal banger.  It is mass = how long it holds the heat.

This new design of a slit side banger will not use a standard carb cap, but more of a marble.  The air does not come from the carb cap, but now comes from the slit.