Gpp iphones are not fake, but are usually refurbished iPhones coming from (japan, korea or china)
Take note GPP chips are used to bypass the carrier restrictions that iPhones have. Which is a good thing.
The downside tho is it has limited supported which means you wont be able to use LTE data in countries offering it
And your stuck with 3G, second this will not work when new softwares will be released by ios so you would need to buy
A new gpp chip would be more costly.
Hope this helps.
Good Luck.