Connecting ESP-01 (ESP8266)

I am preparing my first ESP8266 project. I am not sure, how to connect an ESP-01 board to Arduino UNO - I can see warnings all over internet, that only 3.3V should be used. On other hand all tutorials I have seen connect RX/TX wires directly between an Arduino UNO board and the ESP-01 board. Is it correct or a logic converter 5V - 3.3V should be used for RX/TX signals?

You can probably get away with connecting them directly like so many others have done. I've never heard a report of this immediately destroying the ESP8266. As for the long term reliability, I can't say. The logic level converter is the safe choice. If you use the correct logic levels, you don't need to wonder whether subjecting the ESP8266 was the cause of the problems you're certain to encounter during the course of this project.