  In this paper, we provide a new characterization of Keisler's order in terms
of saturation of Boolean ultrapowers. To do so, we apply and expand the
framework of 'separation of variables' recently developed by Malliaris and
Shelah. We also show that good ultrafilters on Boolean algebras are precisely
the ones which capture the maximum class in Keisler's order, answering a
question posed by Benda in 1974.
