The expeditious bracelet is an opal bracelet enchanted with the Lvl-1 Enchant spell.
, When worn, the bracelet provides a 25% chance for the kill to count as two kills toward the player’s slayer assignment (but does not grant additional experience). That is, on average, the bracelet activates every four monster deaths to provide the player 5 kills towards their assignment. Thus, the bracelet can be used to speed up slayer tasks the player does not particularly like doing. Note that the bracelet needs to be worn only at the moment you defeat your opponent for the effect to occur. This means that for the rest of the fight, other bracelets or gloves can be worn such as the Barrows gloves.
The bracelet has 30 charges, with one charge used each time it activates, and will disappear when all its charges are used. The number of charges is linked to the player. The only way to reset the charges is by breaking a bracelet, via right-clicking it.
You need an average of 1 charge per 5 assigned Slayer creatures or a bracelet for every 150 kills, so, to calculate how many bracelets to take on your Slayer trip, divide the total you need to kill by 5 and make sure you have at least that many charges with you.