Bit late to the discussion but been researching Panhard bars and watts some, since I want to keep a leaf spring setup on my beater project BUCK.
Not sure if I'll do either BUT was reading another book by Carroll Smith - Tune to win And he basically says the Panhard for leaf springs is simple and good enough, watts isn't worth "the theoretical advantages" & complexity. Also he talks bout the design and set up of a Panhard and as mentioned by Erik, that one in the link is not good based on what I've read. IF I decide to take the time & money to fab either I'll build a Panhard setup but I got a few other ideas I wanna try when I get around to it.