MEI checker is a 'Bash & Python' script to help you understand whether your IMEI (and also your phone) is standard(fake) or not and it will also help you to know about the quality and the country where your phone has been manufactured in.
If script said you that the IMEI is not VALID don't think about it and just go for next phone, So it is useful BEFORE you buy.
NOTE: What I mean by validation, is the process of checking IMEI number format and verifying it based on standard formula and not the identity check for your phone based on original manufacturer.
The International Mobile Station Equipment Identity or IMEI is a number, usually unique,to identify 3GPP (i.e., GSM, UMTS and LTE) and iDEN mobile phones, as well as some satellite phones. It is usually found printed inside the battery compartment of the phone, but can also be displayed on-screen on most phones by entering *#06# on the dial pad, or alongside other system information in the settings menu on smartphone operating systems