AFAIK you can only offset one account with First Active. With NIB we have 5 accs offset - 3 Current Accs and 2 savings accs.
We had a nightmare getting it set up with NIB, but hopefully now its all sorted. Still early days so will wait and see how the savings stack up.
BTW we actually switched from FA, and our repayments are about €140 less pm, and the term is already 5 years shorter, so in that we are certainly seeing a difference.