It's not as space efficient as the HHKB layout, but it's better than, say, the Model M Mini and SpaceSaver II layout, yet offers full functionality, with only the numpad requiring a mode shift (as opposed to the HHKB, where I might as well duct tape the damn Fn key down, looking at how it works, and my typical usage pattern.)
And, note that the editing block maintains its shape, and the arrow keys are slightly offset.
This layout's my favorite laptop layout, too. (And, Dell's used a variant of it in the past on Latitudes, which is the line that they compete against ThinkPads with.)