For reference, NAD is an electron carrier in cells (https://en.wikipedia.org/wiki/Nicotinamide_adenine_dinucleot...). The (+) stands for a charge on the molecule. Roughly, it is involved in oxidative metabolism, among many other processes.

Calling it 'good for energy and metabolism' in one of those wishy-washy ideas about how the body works. It's not clear how adding more of one component of metabolism will affect how energy is moved around and released from food.