Resetting a jailbroken KT3

Hello there.

I'm selling my KT3 and I want to clean its memory beforehand, leaving nothing behind. What I don't know is what will happen if I use the reset option, considering the device is jailbroken—will it brick it or something?

Moreover, is there a way to "un-jailbreak" it? And which folders/files must I remove in order to remove all addons I've installed after jailbreaking it, to remove anything tying the device to me before selling?

Thank you.