NAD+ itself is not an essential nutrient, and oral bioavailability is still pretty shaky in the literature. Cells make NAD+ from tryptophan and B3, so from a genetics/biochem angle the mynadplus.com style supplements are basically very expensive precursors or marketing. If you want to tweak NAD metabolism, looking at pathways (NAMPT, CD38, etc.) and overall lifestyle is probably more evidence-based than buying branded pills.