Advatages- tunability
Disadvantages- you gotta rebuild them every so often--- cost to upgrade
I can definately say that if you don't get them you won't know what your missing, but if you do get them you probably won't regret it either.....
Just some advice--- if you haven't upgraded anything already and think you will also want to upgrade to aluminum shocks and universals, then just save up and get a TAO4-R kit it will be much, much cheaper in the long run........