SHEIN and Temu aren't the innocent, budget friendly alternatives you may think them to be. They're both companies rooted in exploitative, inhumane business practices, including dehumanising working conditions and slave labour. There's a viral video going around that shows a large amount of Temu factory workers, barely clothed and being observed by security guards, as they sort through thousands upon thousands of packages.
These companies thrive on enticing people from lower socioeconomic backgrounds into overspending by using game-like incentives (interactive spin wheels to increase discounts, minigames revolved around adding more items to your cart or wishlist, etc.) while using their apps. These apps are carefully and consciously designed in such a specific way that encourages people to feel pressured into overspending for fear of missing out on an unmissable deal (this is a common business practice that extends far beyond SHEIN, Temu, and other fast fashion companies).
Their apparel and clothing is made as cheaply as possible with poor quality material (which ultimately means these items have to be replaced sooner and thus help perpetuate a toxic consumerist cycle) and often using stolen art and designs from independent artists. Do yourself a favour and stop supporting the toxic fast fashion industry. Thrifting, upcycling, and learning to make DIY clothing are infinitely better alternatives and help to support your local community.