[ainarssems]

That one looks like it's just a resistor with wires and plugs that sits between fuel pressure sensor and ECU. All it does is tells ECU that fuel pressure is lower that t really is and ECU then compensates for either by raising fuel pressure or increasing injection duration and dumping more fuel in engine. Not the most elegant way to do it. You could probably do the same just putting resistor in there for couple pennies.

There are better plug in boxes(and more expensive) but nothing beats custom tune.