Need to replace iPhone screen. Are aftermarket parts OK? I have an iPhone 4 or 4s (not sure which) with a cracked screen that a friend of mine asked me to replace.  I see online that you can pick that part up for $20-$30, but they are all "aftermarket" (i.e. non-Apple) parts.

I've never replaced the screen on an iPhone before, but non-Apple parts in other areas (like laptop power adapters) have always given me cause for concern.

Are aftermarket knock-off parts OK?  Do they work as well as Apple OEM parts?  What is the quality like?
Be willing to spend about $40 for the more expensive ones, because in the end, they'll be worth it. The parts work well, but the ribbon cables are ridiculously easy to rip and tear, so be extremely careful.

The cheaper ones usually have thinner glass, thus cracking easily. Also, make sure you specify either CDMA or GSM when searching for parts as the CDMA parts are different from the GSM ones, and they're not inter-compatible.