They are retention holsters, they allow for a fast draw while still holding the pistol securely and prevent others from grabbing it.
This is mine, notice the big paddle behind it? That fits between my body and belt, it’s thick so if you try to rip my holster off you will need to break my belt because the holsters not going anywhere.
As for grabbing my pistol and drawing it yourself there’s two features preventing that. The first is the thumb break shown in the above pictures. To release the pistol you must slide the thumb break to the rear as shown. Since this part is against my body you are going to be fighting with me if you want to push it to release my pistol.
The next feature is a front sight snag shown above with the red arrow pointing to it. If you don’t pull the pistol straight up the front sight will snag on a series of V cut outs below the indicated point. This will bind the gun tightly into the holster preventing anyone from drawing it till you rock it free. So if you run up behind me and grab it, even if you press the thumb break, pulling it out of the holster from your angle without jamming the pistol in the holster is going to be next to impossible.
You have to practice with this type of holster to keep from jamming it yourself but once you get it into muscle memory it’s quick and instinctual. Just please practice with a empty weapon.
—