Hey Sean; Welcome to Permies!
I have not used foreverboard . In fact, before your post I had not even heard of it (new products come to Montana very slowly)
After reading about it , I would buy this for any new construction.
They don't seem to want to give out prices... I'm sure its not cheap, but if it is impervious to
water damage or mold, it would pay for itself in the event of flooding.