Yes it will eat your Fish, Yes it will sting your corals, but there are chances your fish are smart enough to stay away from it, the haddoni i had only ever ate 1 fish that was severely sick, never bothered my healthy fish, but thats not to say it wouldnt happen, IMO... put the anemone in first so it can walk around and find its spot first, then after it settled in and stays put for awhile then start adding corals and stuff.. if thats not the option always just closely monitor it while it moves if its starting to move towards coral, be sure to clear is path so it doesnt sting the corals...
Haddoni's like to stay in the Sand... S. Gigantea's like to go on the rocks..