The amulet versus stone is a SLASH'EM item which prevents stoning much in the same manner as an amulet of life saving. Unless it is cursed, instead of vanishing after saving your life though, the amulet will change in beatitude (blessed to uncursed or uncursed to cursed.) Thus, the same amulet can save your life multiple times, especially with a supply of holy water. Overall, it is generally inferior to an amulet of life saving, however, due to SLASH'EM's stronger stoning monsters, it can be a good item to have on hand if, say, a basilisk blocks off your escape route or an asphynx attacks from under that chest you were trying to loot. Also, if you have another source of reflection and drain resistance and haven't found an amulet of life saving, it's probably the best one to be wearing to prevent YASD.
Due to a probably accidental line of code, a player vampire's bite attack, which is normally deactivated for stoning monsters, will be reactivated while wearing this amulet. This can make it easy to lose to a player who takes that chickatrice lightly because "I'm stoning resistant!" The main way to prevent this is to read battle spam messages carefully (which you should be doing anyway around a stoning monster, if not always.)