I avoid all the made-for-dropship type stuff whether it's sold by Temu, amazon or third party sellers on otherwise reputable retailers' stuff.
I like the fact that in the UK/EU we have regulations about stuff which I'd never even have thought to check, like lead content in clothing, or how easily removable batteries are from children's toys, or what thickness the wires have to be inside an electrical item where you can't even see them. There's absolutely no way that an average consumer can be aware of every single possible safety standard, I know I can't keep up with them, I like the fact that in general, I don't have to because I can safely assume that if a product is sold it is broadly safe.
And yes I know that products produced for reputable manufacturers can still have issues sometimes (e.g. the asbestos found in play sand products) but these incidents are few and far between because of the combination of the regulations and the fact the companies value their reputation. The random company you've never heard of which is selling these items produced on a backline by a nobody doesn't have a reputation to protect. As soon as they get reported to any kind of enforcement agency, they just dissolve and pop up under a new name. They don't care about the safety of their products or anybody using them, let alone the cost to the planet of all this essentially disposable stuff which wears out even more quickly than the poor quality (but at the very least safe) cheap items from e.g. Primark, free magazine toys etc.
You might say well that's theoretical, but it does seem to be true that the products produced on backlines and sold in this way consistently do use materials which are cheap because they can't be used in products for sale to markets which have these kinds of standards, because they are harmful. Or they skimp on electrical safety in order to cut costs. That's why the items are much cheaper. And when they are sampled by consumer safety organisations or enforcement agencies they are frequently found to be dangerous in far higher number than anything which is sold through other, more trustworthy channels. In fact Temu have just been sued by the EU because so many of their products fall short of safety standards.
So no, I don't like them, I would not buy from them. A good way to spot the third party items on sites of reputable retailers (like the Debenhams example given above) is that there will be an almost impossibly large number of items in any category. Usually there is an option in filters to exclude items which are not sold by the website host.
If you do choose to buy items despite this concern my advice would be stick to items with a very simple function, don't get too complicated as it's just more to go wrong. Avoid for items which will be used by babies or young children who still put things in their mouths, avoid for anything electrical particularly items with a lithium ion battery or which will be left unattended. If you do choose to buy something with a lithium ion battery, read up about thermal runaway, be prepared to evacuate (don't fight a lithium ion battery fire), don't charge it in a location which would block an escape route and only charge it when an adult is awake in the same room the whole time.