More flex and less binding would be the obvious plus.
The downside, from what I hear, is that the heims are not greasable and therefore wear out quickly. But, I will say that several people locally seem to love them. But if you ask on this board most people seem to hate Skyjacker entirely.
I have a complete 4" single flex kit I'm waiting to install. The only reason I bought it was the price. I got a great deal on it. I hope all the bad things I hear are wrong. LOL
On another note I've heard a rumor that Currie's johnny joints use the same threads so those would make nice replacements in the future if that is true.
Can anyone confirm this?