The main difference was the ships were designed to escort large vessels and act in concert with them during combat, whereas traditional Birds of Prey used to strike, cloak and restrike tactics.
Two forward disrupter emitters, a single class F missile launcher and four class 2 phaser emitters with arcs to cover the entire ship made up its armaments. It also sported a tractor beam.
They were normally crewed by 14, with room for 26 passengers/troops and carried a single shuttlecraft.
Several further modified vessels were in service, including a commando transport (E-4G) and a drone escort (E-4D).