The best way to take larger dose niacin is with a meal, which extends the release of niacin into the blood over a longer period of time due to digestion, thus helping to reduce the flush effect. The other thing you can do is just take an aspirin 20 mins before you take the niacin. Aspirin helps to open up the capillaries but in a different way(no flush) and this will also help to reduce the niacin flush.
I've been taking a higher dose of niacin for quite a while now, wouldn't be without it.
I've found that niacin, when taken at the higher dose, is perhaps the most relaxing vitamin or mineral that I have ever experienced (Magnesium Chloride comes pretty close though). I always sleep like a baby whenever I take 500 mgs in the evening.
If you haven't got high blood pressure or heart problems then niacinamide (no flush form) is fine to use for all its immune boosting and other health benefits.