Yes, glass chip kits can be used to fix a cracked screen, but only in the following conditions:
- The crack does not cover any of the touch surface (only the bezel area is cracked). Anywhere resin is left on the surface of the device or seeps under the glass can block the electrical signal from your finger and prevent the device from reading a touch in that area.
- The "suction cup" (really, a gasket) included with the kit will likely only be partially attached to the device during the repair. It must completely cover the crack, but may only extend off one edge of the device (it will not work well on a corner) and the hole in the center of the gasket must not cover the touch surface.
These conditions mean a repair is not likely to work with an iPhone or iPod Touch, but may work with the larger bezel on an iPad, especially as most cracks begin near the edge of a screen.
There is one modification to the instructions included with the kits. At the point where you press the gasket sticker to the glass to make a seal, you should also fold it down so that it seals the edge of the glass as well. This is because the metal backing on the iOS device does not completely cover the sides of the glass. You need to seal the resin within the glass and prevent it from escaping. This is why a corner repair is unlikely to work well: it is difficult or impossible to get a good seal over a corner.
The last step of the process requires you to leave the device in direct sunlight, preferably outdoors, to allow UV light to cure the resin. Make sure not to do this on a hot day, or the heat can damage your device. I did my own repair on the day in the low sixties and still had a temperature warning by the time the resin had cured.
Even following these tips, you may end up with an imperfect repair. However, this should be enough to prevent or at least significantly delay the crack from spreading, and thus likely save a much more costly or extensive repair. In my case, the crack is still visible, but only if I remove the protective cover (which I never do.)
It's also important to note that this will void your warranty, but as the warranty doesn't cover accidental damage anyway it's a case of pick your poison.
Unless you are going to never flex the device, you'll want a clear adhesive cover or clear tape to prevent the glass from easily falling out and cutting your fingers or lying in wait in a pocket or bag.
Something like a Otterbox case with a more substantial plastic barrier might be appropriate (or even both clear tape and a thicker plastic sleeve depending on how likely the glass is to fall out.
If you run your finger nail lightly over the surface, you should be able to tell if the underlying layers are cracked or if the surface digitizer layer is cracked and proceed appropriately.
In cases where the digitizer is intact, I have known people to baby a phone for 6 or more months without any glass pieces falling out, so it really depends on how bad your drop was.
Best Answer
You have to replace the whole assembly.
The LCD and the glass are glued together so it's next to impossible for the average repair person to separate the two. (Technically, they can be unglued, but it requires specialized equipment).
These are tough to source and expensive (PN# 661-05095). You may have to get it from a Apple repair shop or surf eBay for a "parts" MBP and salvage the screen.