I perfer having a solid mount. Its going to be more stable and predictable. With a doubble shackle it will act funky sometimes, and you wont always know what its doing.
Plus, without double shackles, mine still flexes fine.
And I still have a bit more travel out of the springs. If I backed up, you would see. I have just about as much travel out of the rear as the front.
I agree I prefer a solid mounts to, I am going to make some shackles that are long enough to replace the double set up using the stock hanger and use 3/4 inch bolts also.