Studies suggest that it has no influence on metabolism, BUT if you take the one with the flush effect your skin gets fkn red and you heat up like crazy, and I mean alone that increase in physiological activity must take some energy and the heat must be produced somewhere and the heat leaves the body over the skin surface and needs to be compensated in the body? No? Yes?
Rather put yourself into cold baths, will burn more calories. Nothing from niacin, it aint no fat burner, it is added in pre workouts just to give a phsyiclogical effect so people think that yea it is working.