Hello all. I apologise if this is not the place for this type of question, which I understand in itself is obscure, but I was hoping that someone with metalworking expertise might be able to help.

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I need to mount some shelves to hold approximately 25 kilograms of weight. I am looking at L-shaped stayed brackets such as these ones. I have, however, seen a massive difference in the prices of these. The ones in the link I gave as an example are extremely cheap (less than $27 Australian certainly is), but are claiming to be able to hold up to 200 kilograms per pair of brackets. To the best of your knowledge, are these types of high-strength bracket cheap to manufacture, and is there much that can go wrong in the manufacturing and quality control process? In other words, are these types of offer too good to be true?

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Thank you in advance!