No - it releases iron too slowly - untreated pure iron nuts are betterKnowing that @Sallstrom is a crazy Swede and also knowing he hangs out with crazier Swede @Lasse , I'm inclined to think he just throws a few chunks of this into his sumps!
When I had freshwater tanks with plants in the stone age - we often use this untreated iron nuts as iron sources I´m sure it works as well in Saltwater - but it need to be untreated iron. It will probably catch some phosphorus too (win - win)
Sincerely Lasse