This one's not as good as it looks - checked it out at the MS store near me - it attaches to the base of the type cover, not the SP3 itself, which means it's hardly holding the device at all when open. Knock it over by accident or something while it's in the case and the SP3 will go flying as only the type cover magnet is holding it in place.
@Simon Kimber - you have echoed my dilemma thus far. I'm about to just settle on a skin (I prefer brown leather like but can't find any on Amazon) and a professional sleeve that isn't too expensive to carry in my leather saddle bag.