Hybrids (and full ceramics) have a huge variety of uses. They’re also used where you have high heat, when electrical arcing is a problem, where higher speeds are required, where no lubricants can be used (ie space), and (probably most commonly) where weight is an issue. In extremely high speed uses (ie jet engines) centrifugal force of the steel balls becomes a problem… so the lighter weight ceramic works well.
Not worth the cost for yo-yos. Yes their coefficient of friction is slightly lower, no it doesn’t make that much difference for us. We don’t deal with any of the problems they were designed to solve.
Full ceramics are extremely fragile… they work in yo-yos, but they also break very easily… and by break I don’t mean you need to clean it again, I mean actually physically break into pieces. High quality ceramic bearings run in the $100+ range (cheap Chinese versions can be had now for around $20) and will give you no significant bump in performance over any other yo-yo bearing.