They are great, though expensive, all the new vehicles have them but seriously an unnecessary expense for a daily driver, new u joints and a rebalance and you'er good to go.
Whats the plan for the car?
For the price they are these days, they are great if you have some vibration issues and such you are trying to get rid of. In terms of adding power, put the money elsewhere.
I have one in my car, but only because it was $140 or so when I bought it.