As above - searching will find plenty of info on it.
Suffice to say that for those $ you should NOT expect something that monitors EGT and adjusts turbocharger vanes etc etc.
In fact this "chip" is trickery in a box. It wires in to your accelerator pedal and the fuel rail pressure sensor. As you press your foot on the pedal, the chip reduces the return value from the pressure sensor, causing the ECU to crank the fuel rail pressure up higher.
Since there's no monitoring of the EGT, a chip like this in a Nissan diesel can cause problems if you flog the guts out of your car (because they run so hot anyway).
You WILL get more beans from it, and more smoke, and more receipts from fuel stations.