I don't have much experience with mini humbuckers, but I did just get an SG with mini-hums, and they are so cool! These things are new, so they're like Gibson mini-hum reissues or something. They have low/moderate output, similar to a P-90, and they bite and chime like a P-90 with a little more low-mid thickness and a lot less noise. Great little pickups IMO. They don't drive my amps very hard though, so they're not good for very hard rock or high gain sounds without help from a clean boost or overdrive pedal. But for classic non-metal humbucker sounds, they do really well.
I don't think mini-humbuckers fit a traditional humbucker body route though. Check on that. I could be wrong. With the mounting rings, mini-hums are about the same size as a P-90, which won't fit a normal humbucker hole.