Review on Reese Towpower 74797 Coupler Repair by Yousef Clark

The product looks worn or slightly used (tarnished lever, rounded nut and other metal abrasions, locking pin that has lost the ability to close), came without original packaging, no instructions, and after downloading the instructions from Reese it has an additional part (3rd picture below right). An extra part can keep the nut from loosening after the parts are assembled and the springs are relaxed (4th pic)? I think it would work for my situation (mainly for garden use) but if it's a trailer for regular road use I would never risk used parts that don't have identifiable part numbers to make sure they fit. Otherwise the product itself if in the original packaging is probably a good product so will refuse to give it less than 4*.