Originally ordered an IS. The way it was cut didn't really fit right, didn't cover the bezel, and the one I got had a giant crease or scratch or something over the front. They shipped me a replacement and I still have it, but I bought a BSE.
I will say that the BSE's are cut much better (closer to the way the iPhones actually are, so the gaps are narrower or almost non-existant and lines up better than the IS) and while the BSE back is more difficult to apply than the IS (the way the corners on BSE are designed, it's tougher to make sure everything lines up), once you got it where you want, it's easier to get it to look good. Three attempts at reapplying the IS corners and I stil could not get the flaps to not bubble up.