They're good for carrying when you're wearing something that can't hold up a gun belt - like gym shorts and a tshirt. Or for when you need to be discrete - like working a job where carry is "against the rules" but 100% legal, and a belt holster would be too likely to be made.
They're good for an "everywhere" gun, because it's pretty comfortable, and you can keep it as a backup when you've got your shoulder holster on.
They aren't my favorite carry method, but it grew on me.
It's not uncomfortable, I carry it with a Taurus 85 and sitting down is no problem. It does NOT point at anything but the floor. It's like wearing a fanny pack, inside your pants. Imagine an apron with a pocket over your crotch, now put your gun in your pocket, pointed down. Same thing, but inside your pants.
I was skeptical. But SmartCarry offers a money back guarantee, and it's only $50, so I tried it. Within a week, I had figured out how to adjust it comfortably, and it works great.
Oh, by the way, I make custom leather holsters, so yes, I'm endorsing my competition