Comments made to our Dark Souls Wiki
Coolest armor in suvh a light weight, after Ninja set(shadow set) and sealer set (red one from wheels in Blighttown) this is my favorite now
Onstein is a anor londo god.
Need to add that Ornstein's Helm, Armor, and Leggings all cause a minor reduction in stamina regen (each)
Thief Mask pairs well with the set if you also happen to think the helmet looks dumb
For those who want the plume nexusmods com/darksouls/mods/1635
all this mentions is that, "If you kill Ornstein first, Domhnall will sell Smough's armor instead". where it implies that you will not receive the armor post battle, it is not actually stated that you have to purchase whichever set you are allowed depending on the battle's outcome.