In retrospect, I regret not buying the single with the add on option since I too only need the double capability once in a while. I suspect the single would be more manageable for single bike use (which is most of the time for me), but I did not understand the wisdom of that originally.
I used the rack for only the second time today, and other than the slightly clumsy process of folding and unfolding the rack it is a pleasure to use. It was also a little unwieldy to remove the bike as I felt like I needed a third hand. I used my chin to balance the bike (what could possibly go wrong doing that?) while I released the 2nd arm. There must be a better way, but then again, I'm new to this thing.
Still, I'm very happy I will not need the damn fake crossbar again which was required for my former Hollywood rack.