Single desktop exposé works well, I use it instead of Mission Control.
However, the way Mission Control (and I think the original Exposé) work is that if you press the hotkey while already in Mission Control, the window under the mouse pointer gets selected. With the Single Desktop Expose implementation you have to left click, and pressing the hotkey just returns to the previously focused window.
edit: another use case is activating it via the trackpad (with BetterTouchTool, etc.)
This is less comfortable/intuitive/consistent especially if you program a mouse button to trigger exposé.