Calling it a "teensy with wifi" is not a horrible description. There's obvious differences like the number of IO pins, but speed/memory are comparable. But yeah, it's a good chip to play with and presently the least expensive route if you want to go Wifi with your projects.
I've played with the ESP8266 and Lua together but not with any of the NodeMCU boards, but then those NodeMCU boards are not much more than breakout boards (with USB) for the ESP8266 module. With an ESP8266 and any USB to serial converter you would have the same functionality as the NodeMCU boards. It's a bargain to avoid that breadboarding hassle though.