for a good manifold it needs to be at least 3mm thick if made out of that material and have proper braces so the manifold isnt supporting the full weight of the turbo,otherwise you will experiance what alot of other bargain hunters have experianced-cracked manifolds and in some cases the flange will fall off altogether
i would only ever use either a genuine trust manifold or a custom one knocked up by someone who knows what they are doing,it all depends on your budget,i firmly beleive in buying the best you can afford,it always works out better in the long run