Review on HiLetgo HC-05 Bluetooth RF Transceiver Module - Wireless Master Slave Integrated Bluetooth Communication for Arduino with 6 Pin Wireless Serial Port Connection by James Holker

A little scold. In short, if you think about it then buy it. It works great and is a great price. IF you have thought about buying another type of module, be careful. One module that is *blazing junk is the AT-09, also known as the MLT BT05 or 4.1 BTE module. You can search the web for a manual (one of which has been translated from Mandarin, but you'll have to spend some time finding it) and it will show ̶h̶o̶w̶ ̶its ̶s̶u̶p̶p̶o̶s̶e̶d̶ ̶t̶o̶ ̶t̶o̶ ̶w̶o̶r̶k̶ ̶w̶o̶r̶k̶ confusing pinout terminology. You'll have luck setting it up and putting it in "AT" mode, a necessary step for it to work properly. I haven't tried other module types but I have no doubt there are others like the AT-09 so I can't stress enough that you are buying a faulty module or a known bad module type like the AT-09 MLT BT05 4.1- BTE module. Thanks for your time.