I'm trying to tighten a slip joint zinc nut where a leak appears to be coming from. I found this particular wrench which seems to fit the bill (shown below and here). How is this tool better-suited for the job than a standard adjustable spanner/wrench?
I bought one of these wrenches you show many years ago and have used it only once. They are a pain to use but will get the job done. I prefer an adjustable pliers made by Crescent or Channellock. Some people call them "tongue and groove pliers". but plumbers and fitters just call them Channellocks. Tradesmen that work with piping and plumbing have them in many sizes the most common being a 12" pair. These are mine