There is a 30 Attack requirement, you must also complete The Fremennik Trials quest to wield the blade. It has the same stats as an adamant scimitar, but with the speed of a longsword, thus making it inferior to the adamant scimitar. Bardur, located in the Waterbirth Island dungeon, will trade you cooked Sharks for Fremennik blades, Fremennik shields or Fremennik helms.