How safe are usb wall adapters from China?

I'm looking to source some usb wall adapters on aliexpress and am wondering about the safety of these plugs since I've read articles saying they can potentially catch on fire.

I'm looking to use the usb wall adapater to power a nodemcu/arduino so power consumption is pretty low.

The adapters are something like this:

https://www.fasttech.com/product/1035300-1000ma-usb-power-adapter-wall-charger-black

http://www.dhgate.com/store/product/dual-usb-wall-charger-us-plug-2-1a-power/249581554.html