  We motivate that the start-up of the B factories has opened a new precision
flavour physics era, with an important effect on model building. Using as an
example a left-right model with spontaneous CP violation, we will show how the
inclusion of the new experimental data on B physics observables, together with
the old observables coming from kaon physics, has significantly widened our
capacity to strongly constrain the parameter space up to the point to exclude
models. On the contrary, using certain hypotheses, mainly concerning isospin,
we discuss how theory may help us to `test' the data on charged, neutral and
mixed $B \to \pi K$ decays once experimental errors will be reduced.
