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With respect to whether it's advisable to get smaller items - we would say that it isn't the size, but rather the savings you can get from shopping the items from the U.S., especially for designer goods and specialty items (i.e., baby necessities, hobby items, etc)
Example of Savings on a small item:
If a certain designer t-shirt that you like costs SGD150 here, and just USD35 in the U.S., then it definitely makes sense to ship it over, even if it weighs just 0.5kg, because you'd get an instant discount of over 50%.
Another situation in which it's good to shop online in the U.S.: If the item is exclusive and you can't get it in Singapore