I use a roof box. It 100% protects the bike and there's loads of room....A useable box won't be much more than a Thule bike rack but you will pay a bit more in petrol but not much more. The other thing I like is you can leave your car without worrying about getting the bike nicked.
I use a roof rack similar to what the OP asked about. I transport bike regularly and it works good.
Over ver VERY long distances I it surly is bad on gas milage. I bet the above quotes, "box" is better on gas than a roof rack.
Not to mention the car and bike woun't be blown around when you get high winds or pass a big transport truck.
I am always worried that it is damaging my bike to have those types of heavy forces on it.
I am now consering the "Box" idea.
The roof rack is great fro shorter distanced in my opinion. But over lond distances it is terrible on gas, I worry about getting rock hitting the frame and heavy gusts of winds make me worry.
Just my thoughts.