I love to use the Little S on greenies who hate bits, horses who need to lighten up in the mouth, those who need noseband action but not a full-fledged combination bit, horses who are learning to neck-rein but are confused by shanked bits, those who know the basics of lateral movement but still need some work on it; in the training pen, while trail riding, and on some barrel horses. Needless to say, it's extremely versatile.
Pulling on the reins rotates the "S" shank that gives the hackamore its name. This tightens the curb chain and brings the noseband down slightly. I consider this to be a rather mild hackamore with an almost bit-like action.
It's good for both direct reining and neck reining (I actually try to teach neck reining in a snaffle bit, but the bit's action makes this rather difficult. As you put your rein across a colt's neck, the bit pulls on their mouth slighlty, confusing them and giving them a conflicting signal. So I switch to a hackamore or halter to test how much they know, and suddenly they get a lot more comfortable neck reining because there aren't two commands going on at once). And, for a hackamore, it has a suprisingly good amound of lift, bend, and flex.
The short, curvy shanks make this a very gentle hackamore when compared to several others. You'll often see this hackamore sold with a leather noseband to replace the abrasive rope, and this increases its gentleness.
Now, not all horses like them...
Read more: My Own Informative Bits and Bitting Thread