I owned a BMW F800ST. That bike had very lean fueling at idle and was easy to stall. A Boosterplug did, in fact, improve the way the bike ran. The guy who invented it and originally sold it also owned an F800ST and developed it for that bike. He eventually passed the business on to someone else. What the device did was fool the fuel injection into thinking that the engine was colder than it actually was so that it would enrich the mixture, curing the lean stumble. It was a simple device consisting of a resistor and another component that I forget. It was set up to only affect the lean part of the fuel injection map. After someone cut one open and revealed the circuit, others copied the basic idea but used only a resistor which had the effect of enriching the entire map causing fuel consumption to rise. While it worked for the F800ST, the Boosterplug is grossly overpriced for what it is.
The NT has none of the fueling problems of the F800 and absolutely does not need a Boosterplug.