The main difference being that the more traditional model, featuring pro-rata allocation and collection ofpayment for order flow, is more geared towards one facet of the investing community, comprised in large part by retail investors who are using options limit orders and other very simple strategies.
The IMF's mission was to give countries temporary short-term loans so they could put their economic houses in order, coping with temporary balance-of-payment problems without resorting to destructive tariffs or massive devaluations.