I have the larger version of this on my Galaxy Tab.
Had it now for a good few months and it is very good.
I was a little concerned at first with the stand at the back. Being made of plastic I had visions it would snap off but no, it's held the Tab in Landscape mode very well.
Also, the edges are made of rubber with a textured surface, this makes holding the Tab feel very stable in the hand.
If this case for the SGSII is anything like the one for the Tab I won't hesitate in getting one of these for the SGSII.