They are FANTASTIC if kept busy and well trained.
They are happiest when working, or going to work with you in your ute and supervising building sites and such.
But...they're nippy...bred to nip at the heels of cattle (hence the heeler) and tend to do this if you aren't doing as told.
Kelpies are great, too....
But CRAZY if not working sheep.
They are "eye" dogs...ie they control sheep with their gaze, so not nippy, but sooooooooooo manic: