The notation is presented somewhat confusingly; this definition given for +:

  \x. \y. (\s. \z. x s (y s z))

Isn't different from

  \x. \y. \s. \z. x s (y s z)

And usually syntax sugar is assumed such that you can just say:

  \xysz.xs(ysz)

Which is much easier to read.

Personally, I find the textual, symbolic representation much easier to reason about; my eyes just glaze over the circuit diagrams.