My son has cracked his screen twice and most recently, I cracked my screen so this was my third time replacing the screen on a 4s. Each time, it's taken less time for me to complete all the steps and this time because I knew I'd be buying a new phone within the next 4-6 months, I asked for the C-Stock screen. Let me just say that the C-Stock screen does have noticeable scratches all over the screen, but this does not interfere with the functionality of the phone and I'd say if you are close to getting a newer phone, save the money and get a C-Stock screen.
Repair went very smoothly but it helps that this was my 3rd time doing it.
The only advice I have to pass along is some helpful hints that others have shared that make this repair go SO much smoother.
1. Get two pieces of duck tape or packing tape and tape it beside you, sticky side up, to the surface of wherever you are working. You can put the screws on the tape in order of how you take them out of the phone and they don't move and it makes things go little quicker when you're reversing the directions.
2. If you're not sure about the tools you have, buy the kit that includes the screwdrivers and the prying tools...again, they make the job easier because they are the perfect size and they are magnetized.
3. Follow the directions exactly...don't veer and if you get stuck, go to YouTube and see if you can find a video. Had to do that the first time because the battery can be a little tough to pry out.