This recent review of NAD+ generation gives us a renewed overview of this complicated subject. Because it is relatively understandable for us non-biochemists I place a link here.
The authors do not value the supplementation of NAM, but allocate a possible upside to the production of NAM after NR/NMN supplementation.
No mention of poor bio-availibility of NR/NMN.
https://www.ncbi.nlm...les/PMC6145238/