There is a section in "Breastfeeding and Human Lactation" by Riordan and
Auerbach that describes information about the major pumps on the market.
I also have those other brands available for demonstration (I use balloons)
so that moms can see the difference between Medela, Double up, Ameda Egnell,
and those easily available.  The pumps usually sell themselves.
Ruth Solomon, RN, IBCLC