I can't comment on the fit for a 4S, but I can tell you about the case. I've had one on my iPhone 4 for close to a year.
Overall, I've been quite happy with it, but it's not perfect. It looks great, and feels nice in the hands. It leaves all the openings, speakers, etc. very well exposed, so it's easy to use. I have not noticed any flash washout, but I rarely use the flash, so I'm not the best judge.
On the other hand, the case has cracked and broken a bit at the top, so I need to replace it. Also, after a year of use the back is somewhat scuffed, so it's not as sharp looking as at first.
I just ordered a magpul executive field case to replace it, based on the many positive reviews here and elsewhere. I want something with a tiny bit more substance, in the hope that it will make the phone more comfortable to hold. I find the current iPhone shape is a bit uncomfortable on the hands, would prefer rounded edges.
I have been happy with the incase snap, and you will probably like it. I guess all cases have some limitations...