I bought mine according to the size chart, and its waaay too small for my breasts. The hands free aspect is great, but I end up with deep imprints from the compression.
After trying so many pumping options, this is perfect! It sits comfortably on my bra without adding bulk since it uses the existing hooks, doesn't fall down, isn't bulky, and I can get large funnels through the slits. Don't get any other pumping bra - get this one.