Bristle is still worth having actually. It increases the dot damage of Song of Torment which is an overall gain in damage. It's best used like this. Bristle:Off Guard -> Song of Torment. Song of Torment goes from 300 potency total to 450 potency total. Really the only time using Bristle is worth it unless it is a phase where you can't target anything. In which case you'd probably use it on Song of Torment anyways.