i loved niacin flushes, the intent being short term therapeutic oxygen and nutrient delivery to previously starved tissues. not sure about keeping it up long term.
my diet is now full of excellent sources of niacin like chicken, tuna, mushrooms, turkey, venison, halibut, and grass fed beef (that's listed highest to lowest, around 8-16 mg per serving)
previously as a vegan there is just no way i had sufficient intakes of excellent vegetable sources to hit anywhere near a daily requirement. (mushrooms and asparagus, 1-3mg per serving but again the mushrooms have around 3mg and the asparagus around 1mg). the supplements were definitely merited in the early therapeutic stages.
so yes, niacin may be useful