So I have only killed Garry on LFR but I have a question about looms. I understand that on Flex and higher he drops BoA Looms from 90-100. My question is what does it mean when it says that the drop is now guaranteed the first time. If I take my Windwalker through does that mean that he will for sure drop that agility staff? Or if I take my hunter through flex he will drop the bow? Is it guaranteed to drop an heirloom your first time? Or the exact heirloom for that class?

(P.S. I know a while ago on the PTR they were messing around with having one set of armor that changed depending on your spec. Is that still true? Or do you still need two sets of armor?)