So if I have to interference issues there is no advantage to going with boomerang shackles?
Correct. The concept of a boomerang shackle is that as the suspension compresses during up-travel
the spring flattens out and pushes the shackle back and upwards. In general the amount of up-travel is determined by a few factors such as if and where you've installed bump stops, how much compression can your shocks handle, and does the shackle interfere with anything
Shackle interference typically only occurs to the front shackles. If your front springs have any useable amount of positive arc to them, ie all "lift" springs, then the shackle will interfere with something
before the spring flattens out or encounters negative arc. The reason why this usually only occurs with front shackles is that most truck frames have a narrow front section and a wide middle and rear section. The frame is narrow in the front to allow room for the tires to turn during cornering without interfering with the frame. In the case of a Toyota frame, the frame transitions from this narrow section to its wide section right in the location of where our front shackles are mounted to the frame. The result is that the shackle is likely to contact the frame (or body mount or rock slider leg) and put the leaf-spring in a bind where its very difficult for any additional up-travel to occur. This is where the boomerang comes in hand: It moves the shackle plate away from objects in an attempt to maximize shackle mobility.
If you need one or not will depend on how your suspension is set up and if you are going to encounter any sort of interference at the front shackles.