Is Niacinamide comparable to Nicomenthyl 20 as a skin microcirculation enhancer?

No. Niacinamide, unlike Nicomenthyl 20, has no vasodilating activity, is not a microcirculation enhancer, because it barely permeates the stratum corneum layer of the skin (Sara et al., 2008), and its skin absorption is not effective enough to reach the microcirculation of the dermis, as per the graph shown below.

Niacinamide Skin Microcirculation