Heavy duty, but not modular.
Crutchfield Customer Review (What's this?)
It wasn't what I expect. It's heavy duty and secure, but I was expecting the aeroblades to attach separate from this piece to the roof of the car - therefore making it easy to take off the rails if I wanted to attach something different (kayaks). When you tighten this to the piece that attaches to the rail on your car it has a lever that applies pressure to the Aeroblades - keeping them in place. This makes it impossible to easily change out the blades or be able to adjust the blades (centering them) when attaching. It's a 2 person job.
Pros: Heavy Duty
Cons: Poor Design, Not Modular