RALLER,
This isn't about the shackles you are considering, but years ago I installed some BF Goodrich Velvet Ride shackles on my 2000 model year truck. They did improve the ride a small amount, but not enough to warrant the trouble to install them. In 2000 I paid $160 for the pair. If someone gave me a pair today I wouldn't install them; it was too much trouble for not enough ride improvement.
-- Loren