The Schaller Mini-Lockers, Sperzel Trim-Loks, and Planet Waves Auto-Trims all work the same way. There's a post that runs up inside the center of the tuner post and bears against the string after it's been pulled through the side holes in the post. Tightening a knurled nut on the back of the tuner locks the string in place. It's very effective, and doesn't require nearly the tension some folks seem to think it does. They all look good, are well-designed, have high turning ratios and are well-built high-quality machine heads. You really can't go wrong with any of them.
But, you do have to tighten the locks, so there's where the first differences show up. The knurled nut on the back of the Sperzels is thinner than it is on the Schallers or Planet Waves, so it needs a slightly tighter grip that some folks find uncomfortable. Plus, they only come in satin finishes. So, we kick out the Sperzels.
The difference between the Schallers and the Planet Waves is the Planet Waves units have a bit of a die formed by a flange and the the tuner post that the post turns in, so as you wind the string up, it cuts off the excess string within 180 degrees or less. If you like a neat presentation and don't own a pair of side-cutters or don't want to carry them, this would seem to be a pretty cool feature. The less tools you have to carry around, the better off you are, right?
Problem is, as anyone who's ever owned a pair of side cutters or a knife can tell you, cutting edges eventually dull. Especially if you're cutting a lot of coated spring steel with them, as you are when you're chewing on guitar strings. So, I wouldn't expect that "feature" to last long on those tuners, and the cutting die isn't a renewal part. You'll be buying new tuners when they stop cutting. I would expect the problem to show up on the thinner strings first, and as it happens, the first time I ever used Planet Waves' Auto-Trim tuners, that was the problem I had right out of the box. The high E and B didn't want to cut. I ended up needing side cutters anyway. These were
new parts, not some cast-offs or 2nds or pulls from eBay.
So, I'm firmly in the Schaller Mini-Locker camp.