Forget the Genxt warranty, If Genxt fix your phone free of charge after one year Apple care warranty, then it is fine.
If you buy a phone imported by Genxt or any other authorized reseller, you will get a genuinely imported phone, others might sell you hand carried grey imports. If you buy from a authorized reseller, the waranty claim process will be easier and it makes sure you get a brand new phone. Sometimes other people might sell you a used phone as a brand new one