Completely agreeing with @MartPriest.
- The use cases for 'Mix' type are mostly to self drink and gain the according boosts. I'd recommend getting all milk cups (if you have much of it stored), then flush the rest to get a clean milk combination in the collector
- "how many types of milk there are?" : the same count as current tamable fapets (except goblins), they are assigned on random from the list of known tamings.
A side note, upcoming update will have icons above quicklots, representing current mix (Fapet A , Fapet B, or mix) :3