So cool. The flykly is small and weights six lbs and is easy to install and remove. If you can return it then just order one as a trial and keep it if you like it. You could also work with rocket electronics as they will want to it too.
Since a 16" wheel is so small, the couple of manufacturers that I know will make them, only do it with the motor in a mag wheel. There isn't enough space to lace spokes. However, the link you show from NYCEWheels is for a 20" rim. Mag rim setup is cool until you hit a couple of potholes and bend the rim. Most of these motors are not removable from the rim (bummer!) ; however, the options are better for a 20" wheel
If you want something to ride on now, they Flykly is not available and has no delivery date and only web based service. They have no definite production date. If you have multiple bikes to outfit, then set one aside for when this kit is available and sorry @eDean, Flykly has made it clear they want nothing but internet sales (that is if they ever ship anything) so no local shop will be carrying this kit. Read their website, its very clear on this.