According to Wikipedia, the Breen are a treacherous race who were powerful allies of the Dominion. Their ships have organic components and are equipped with an energy dampening field which they used to great effect during the battle of Chin'toka. The asymmetric design of the ship is fairly unique in the ST universe (the Borg renegade ship is the only other one I can think of). There are no good references for the size of these ships. The dimensions from Ex Astris places them about the size of a light cruiser/heavy destroyer. A comparison with a micromachine Vor'cha is shown below.