These are exactly what I expected, and they work great for the Sparkfun ESP8266 Thing. I'm sure they would also work great for any other board that needed a 10 pin header or more.

Maybe it wasn't the best for my components, but I pressed male headers into these and pressed the male headers into a breadboard. I then placed the ESP8266 Thing upside down on the now upside down stackable headers and soldered them on like that, then simply removed them from the male headers. This way I was able to attach the stackable headers perfectly perpendicular to the board, and with minimal spacing between the headers and the board. This method also did not require a third hand or any such device. I'm not sure if this could have potentially damaged my breadboard, but it seems to work fine and my ESP8266 Thing seems to work flawlessly.

Good quality stacker pins, good to have around.