I'm long on reading and short on experience... That said, the number 1 reason that I've read about is 10% crosslink stands up to chlorinated water better than 8%. At what level of chlorine is 10% resin required? Opinions vary and I don't personally know.
I ordered a "PurTest Iron Hardness Plus Water Test Kit" yesterday (Sunday) and it's already been shipped.
That's not much, but maybe it will kick-start a conversation.
I might need to buy an iron filter and I'm also interested in Afwfilters. Thanks.