Here is a short video on how I build a 1s 21700 battery for a Nanolongrange FPV drone. I prefer spot welding over soldering, it is way more robust. Compared to 18650 you will get a slightly longer flight time. In the last third of your flight you will experience a stronger decrease in performance as the weight of the bigger cell makes the drone about 20% heavier.
http://on.fb.me/unboxingexperience