@Kestevan you can avoid most of the pitfalls by buying a light that is clearly well put together, ideally metal case and rubber seals. Like anything from China the buyer specs to the nth degree the build quality and so it is worth choosing a retailer who has something to loose if it goes wrong. For me Aldi fits into that camp because they have started to flog a decent amount of bike stuff.
As for fires, if you sell many thousands of a product with a battery known to be fussy about charging, in an application where it is being bounced around a lot in the wet, and where any old phone charger can be plugged in you are bound to get some fires. It is sensible to either charge them attended or in a metal tin and I suspect the instructions specify this, not that anyone ever reads them.
The essential problem is that ideally you protect the circuit with a fuse on the board, but of course the fuse needs to be somewhat conservative. So they omit a fuse because they effectively write off the lights in all sorts of circumstances, with the downside that in a handful of cases it will self barbeque.