Temu isn't a new idea. There have been many international shopping apps before. Temu is just currently popular.
Intellectual property law is quite different in China. Some might say it's non-existent, but I think that's an oversimplification and I don't want to get bogged down in an argument over international economic law. Point is, China has a lot of manufacturing facilities, and make a lot of the products you know and love.
It's no secret that once a product is made in China, the designs and details become available to other manufacturers in China (and in other countries, but Temu is a Chinese company). Temu works with manufacturers directly to sell product directly without the markup, marketing, warehousing, etc that come with normal e-commerce.
Benchmade needs to let you know they make knives, they need to create designs that are high quality and people like, and then they have to stand by their product. They also need to turn a profit. Temu just needs to profit, and they are probably willing to take less of a markup in exchange for volume. The low cost is their marketing.
Now when it comes to a knock-off, and this goes for anything, but we'll use Benchmade knives as the example, the results depend on what sort of knock-off you're getting.
The best case scenario is that it's the same design, same materials, possibly even the same manifacturing plant that makes real Benchmade knives. Then you get a high quality knife at close to factory direct prices. Congratulations, you've scored a steal, and I do mean that you've purchased a product that has been stolen. The ethics of that are on you, I'm not here to judge.
The next best possible knock-off is the same design, same materials, and maybe the same manufacturer, but it's a knife that didn't pass qualtiy control standards. It would have become a Benchmade knife, but for some reason it was not made to spec. Maybe the printing was off and you get an otherwise impeccable Bonchmude knife. Or maybe the steel was improperly hardened and the blade will snap when you apply pressure. Provided you don't hurt yourself or get eaten by the bear you were trying to stab, worst case is you're out the price of the knife. Temu isn't going to stand by their product, because it's not actually theirs.
The third possible knock-off is a generic version of the knife design. Seeing the sales of quality knives, the manufacturer decides to copy the design to make something that looks like a quality knife, but make it as cheaply as possible. Plastic replaces metal parts wherever possible, glue replaces welds, and the metal used is referred to as "steel-adjacent." This is going to be a piece of crap for sure, and won't actually be worth the price you pay for it, even if it's free.
Here's the big problem with Temu, there's no telling which is which from the product postings. You see the same generic photo from four different item listings, and the knife you buy today won't be there tomorrow. Even if you order two of the same product from the same manufacturer, you could get two wildly different quality levels. And you're far more likely to get the third kind than either of the first two.
Think of the Temu stuff as disposable. "I'll probably throw this away evetually." It's worth it if you use the thing and don't throw it away immediately. Now, I said I wasn't going to judge, hut the last thing I'll say is that we could all do with a little less waste. Let's all of us think twice before shipping disposable products halfway across the world.
But other than that, if it's "worth it" is really up to you.