You should do a forum search, this topic has been discussed extensively before.
Another disadvantage of an iron keel is its reluctance to absorb impact. Lead is soft enough to give to a collision with a rock or whatever, often becoming misshapen... but that absorbs quite a bit of energy which means less potential damage to stringers, tabbing etc in the area behind the keel. The Iron keel has no give and transfers all that energy quite (too) efficiently.
However job one is to avoid such obstacles, and living with an iron keel is not so bad in these days of effective epoxies for encapsulation, which greatly minimizes the maintenance issues.
Also you should avoid posting the same question in two forums.....