The shelf once installed worked fine. However the drywall anchors that came with it were defective.  I used two of them and they both failed in the same way.  Rather than them expanding to a cross like a drywall anchor is supposed to do, these just deformed spirally without expanding.  Then they spun in the hole chewing up the drywall. I was able to get them back out and then use some from the hardware store that worked fine.  Photo attached of how they started out, and how they failed (the one on the left is failed).