IMHO bottom paint without copper has not been in use long enough and in enough water areas (salt, brackish, fresh, etc.,) to prove that it can hold up. I painted my boat's bottom in October and used a good copper-based paint. Three or so years from now when it's due again I'll have 3+ years of track record of the non-copper based paints.
Mike and Tina
Beachcomber 1995 Sea Ray 550 Sedan Bridge