This is a great product and I have used several of them. However, the documentation is barely adequate. Still, it is adequate. The shipping time was great, however, three of the little boards (small postage stamp with legs) were packed in a box that was about 3"x3"x1". It sounded like a box of gravel. The first time I thought the gadgets were broken, but they survived and worked. Later I ordered more and they came the same way. Would it hurt to insert them into a block of conductive foam? I have never received a small electronic device just lose in a MUCH bigger box.
I decided to purchase this device after watching Miguel's youtube video. You can see an initial version of the board in the link below. https://www.youtube.com/watch?v=EWpr3fpNz88
As you may or may not know, the esp8266 has an unfortunate shortcoming of only having 1 analog input, this chip obviously solves that problem through a multiplexer. The github page was slightly harder than normal to find, but includes the necessary examples for reading one or all inputs.
If you were to desire an Arduino based and thus easy to program, WiFi enabled microcontroller, then you could purchase an Arduino WiFi shield for $100+, OR you could instead get an esp8266 w/ breakout board for $6, A 3.3v voltage regulator for $1, the analog input expander $10 and an FTDI to USB 3.3v programmer $3.
So what you get is very close to equivalent solution for under $20. Obviously there is some effort in combining the components and there are notable differences (not all Arduino libraries with the esp8266, 3.3v logic compared to 5v logic, etc)
My only complaint is that I feel this product could be a little cheaper.