Runescape- why do players pk with a ring of recoil?

Easy question. Well people use it for a number of reasons. Firstly it's effect is that it hits back 10% of the damage taken back to your opponent. It can do up to 500 damage before shattering i believe. That's like 2 and a half sharks. Technically it's kind of like vengeance but vengeance does 75% which is a great deal more allowing your damage to stack. Meaning a large amount of damage in 1 hit basically. A ring of recoil can be the difference between life and death as with poison as i have been killed by both when pking. So basically you should bring 3 rings during a trip of pking and wear one of them until it shatters. Then just put on the second.