how does the that's my bis loot system work?

It's basically loot council with the homework done in advance. Each raider puts in a wishlist of the items they want from the raid, ranked. Officers then build prio lists per item using those wishlists plus attendance and what actually helps the raid most. When something drops, whoever is top of the prio for it and present gets it, and it gets marked as received so they slide down for the next one. The nice part is everyone can see the lists before the raid, so there's way less arguing on the night.