This pouch is a lovely fit for the Samsung Galaxy S3, even with a thin case: I have a thin, plastic Create and Case case (Strange Smoke), and it still fits in this pouch - just. I doubt that it would take one of the silicon cases. The phone won't fall out, even if you hold the pouch upside down by the stitching on the bottom.
The design is absolutely gorgeous. The pocket on the back is very useful if you just want to pop out with your phone and a bank card. The lining is lovely and soft and the stitching around the case appears to be very robust and the design is carried onto the stitching, so it doesn't just disappear before you get to the edge.
All in all, I cannot find fault with any part of this item. At a fiver it is an absolute bargain for something that looks good, is well designed and perfectly functional.