These are a great device but be aware that they will not programme with any camera more modern than a D90/D700 . You are wasting your time with a D7100 or even a D800. The chip just locks up and is useless. You get no help from the supplier other than being banned from more pruchases,. The article on how to do it is years old and as the writer says I only have a D700. If you have access to a D90 or similar fine . Must have a top screen..D40 etc no good. Many lenses need some dismantling and carefull filling of the mount for fitting so check carefully.
The ones I have fitted and programmed using an older camera are fine and the lens then works with more modern cameras.