Goodyear or BFGoodrich used to make a set of shackles that were similar a few years ago. I don't know anything about the "Sulastic" but I did put a set of the other ones on my friends 99' Crew Cab Dually and it made a much smoother ride on the freeway where the freeway joints were. When the truck was loaded it didn't seem to do anything.
I talked to a few people back then and they all said that they made their longbed trucks ride smoother but everyone that I spoke with that had a shortbed or drove around loaded(Camper Shell, etc.) didn't notice a difference.
I considered them for my K5 but since I rarely drive it "unloaded" without camping gear on the freeway I figured the $175 was not worth it.
Another one of my friends also did a set on a long bed 4x4 that had a Rancho Kicker Shock on the passenger side and it made no difference that he could tell.
Again since I don't know anything about the "Sulastic" brand I can't say that they would be the same but the concept is similar to what is already out there. If they really did reduce braking distance and increase service life of components that is where I would be most interested. You'll have to let us know.
