Are either of these tools suitable for tightening the pipe union nut underneath a bath?
Looking at the diagram, I believe you want a basin wrench. It's designed exactly for these bolts in these tight conditions. And the next time you go to replace a sink, you'll be glad to already own one. That said, I've never heard of, nor seen a jaw dropper plumbing wrench, so I was hoping that someone with more plumbing experience would chime in.