I played a '74 Gibson Les Paul Deluxe all through the late '70s (still have it, too), and I also have a Luna semihollow with two mini-humbuckers and a Bullet Tele that I fitted with a Guitarfetish neck mini-humbucker.
The Bullet provides the clearest illustration of the difference between a mini-humbucker and a single-coil because that pickup can toggle between the two with coil splitting. In mini-humbucker mode, the tonal difference isn't stark. In fact, if you're not paying attention, you could think it's just a boost switch and not actually changing the coil structure of the pickup. But if you are paying attention, you note that the tone gains more body, if that makes sense. The mini-humbucker senses vibrations across slightly more string length, so it gets a few more harmonics in the mix. There's slightly more bass, more body or fullness, and more output (seems like ~20 or 25 percent to my ear; what that translates to in actual volts, I have no idea). But the mini-humbuckers still have much of the crispness (or lightness or clarity or whatever else you call it) of single-coils. They don't get muddy or boomy the way standard humbuckers can, especially when strumming chords.
I hate trying to describe musical tones with such imprecise words, because I can only hope others understand them the same way I mean them. But if it's not clear, I really like mini-humbuckers. I wound up with the LP Deluxe in the '70s mostly by accident, but it turned out to be a very happy one for me.