Hitch and Bike Rack (review)

I bought both the Curt Prius class 1 hitch, and the Prius V Hollywood Traveler bike rack from Prius Accessory. Both seem very well made.

The hitch from Curt came with excellent instructions. They said a professional could install the hitch in 15 min. My brother helped me install it, and we are not professionals.

We took our time, being sure to do it right. It took just over a half hour to install. I had not worked on a car in a long time, and never installed a hitch before, but it was not tricky.
I would recommend having a torque wrench for the install. I had not used mine in 20 years, and I was surprised how tight you need to make the 87 foot pounds for the bolts.

The Hollywood Traveler bike carrier was a bit more complex. It is actually quite simple to put together, but the instructions are a bit lacking. In fact I am sure they have swapped figure 6a and 6b.
Again we were careful, and it took a bit more than a half hour. I love how easy it is to remove / install the bike rack from the car. So far I am very happy with the results. I will be taking it out with 3 bikes on a test run this weekend.
During the hitch install I noticed a spot for some accessory just to the left of where the tow loop was. (see picture)
Anyone know what that is for?
I have a 2012 Prius v level 3.