The default Windows Forms SplitContainer doesn't contain any buttons in the splitter, and it has an annoying flicker problem while moving the splitter. The MstSplitContainer extends that functionality by providing several features, such as changing the appearance of the splitter, creating an expand/collapse button in the splitter, and adding the ability to hide the focus rectangle.
MstSplitContainer provides interactive splitters and split buttons. This feature allows the end-user to more intuitively collapse or expand a panel when needed. And you no longer need to use code to control the expand/collapse behavior of your end-users.
Contrary to the standard SplitContainer control, MstSplitContainer allow you to easily build slick interfaces with the look-and-feel of Windows and Office.