Around here they call them "suicide shackles". I've heard of them breaking on the trails. They have also been known to make a vehicle slightly more prone to rollovers. I have also heard of them royally f%cking up spring hangers because of the additional twist they put on the leafs.

I also don't see the advantage of the extra droop because they only droop out when there's no weight on that leaf. This means you've drooped the tire but haven't really added any "useful" (grip-enhancing) flex.

Definitely ask around before you buy those. Your local custom 4x4 shop is a good place to start.