I've been taking Niagen for a couple of months, and I can say that for me it feels much better than niacin or niacinamide. I don't know why (perhaps I have some niacin metabolism problem, or the niacin interferes with some other impaired process such as the methylation cycle).

Also there seems to be some synergy between Niagen and resveratrol and pterostilbene that I can clearly notice. Foods that work well with Niagen are raisin(-bread) and olive oil. Of course, ymmv.