[Q] ebay lens glass gorilla?

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http://forum.xda-developers.com – I have a cracked galaxy s3 screen that I want to replace by myself. Searching on ebay, I found several lens glass for sell under $20. Are these gorilla glass 2 or just standard glass material? I only checked youtube videos and looks fairly straightforward. Any word of advice from people who had repaired their cracked screen by themselves? (HowTos)