Additional units

If you  need additional powerline units, do you have to buy in packs of 2?  That would seem to push people to buy another brand, instead, so they don’t have to buy a 2-pack if they don’t need it… (or am I missing something?)

Nope… that’s the way WD packs them…  But, you’re inclined to buy another brand, as long as it’s “Powerline AV” compliant, it will work with WDs…  :)