Can auto glass chip repair kits such as this item repair cracked iOS device screens? If so, what should I watch out for?
Yes, glass chip kits can be used to fix a cracked screen, but only in the following conditions:
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.
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.