I have the WU-1a, and while it is good, the Nikon software is very poor (I use DSLR Dashboard instead) and the range is limited. I tried setting the camera on tripod next to a bird table, and then hid behind a door 4 meters away... the signal strength was so low I could fire the shutter!
But then as a simple wireless remote, with no obstacles between you and camera, it works great and you can view live view, so for sky shots when the camera is at a funny angle its perfect.