The instructions that came with this kit made it really easy to flash with an FTDI connector. The only issue I have had so far, is that the instructions did not include the details to put in the Arduino software. This may have caused me some issues, although it's possible I set some parameters incorrectly. I contacted the supplier, and he got back to me quickly with the correct parameters and some hints on debugging (and where my issue may have been). I set it up for a new network, used the correct parameters, and everything worked fine. The included Blynk code is well written and a useful basis for whatever you want to do.
The hardware is very energy efficient, can come with everything pre-soldered and ready to go, and has a wide range of sensors on board. Fantastic work! I will be ordering more to replace some old temperature/humidity sensors that I have at work.
In case you are unsure about the Arduino software settings, I used these ones: Board: Generic ESP8266 Module, Flash Mode: QIO, Flash Size: 1M (NO SPIFFS), Debug Port: Disabled, Debug level: None, IwIP: Low Memory V2, Reset Method: None, Crystal Frequency: 26Mhz, Flash Frequency: 40Mhz, CPU Frequency: 80Mhz, Builtin LED: 2, Upload Speed: 115200, Erase Flash: Only Sketch.