Product says it's for iPhone 4 ATT. Means it won't fit the 4S. I'd be very wary of cases that have a small cutout for the mute switch and their own volume covers even if they do say it's compatible with 4S.
I've seen numerous complaints about cases like these not fitting the 4S correctly even though it says it does. My theory is, companies were quick to add that they are compatible with 4S's not knowing that it was based off the Verizon model.
So for now, if you get these types of cases, make sure they are CDMA model compatible.