I have purchased them before and they are usually slightly cheaper than retail. Those that you see with a different packing could be manufactured and packed in a different country, as long as it is properly sealed I would think it's safe. (I will only say that Coz we are here in Singapore)
Another suggestion to buy milk powder at lower price is to stock them up during baby fairs. They always have very good promotions which you can save quite abit if you buy in bulk.
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