Depends on the airline. LH has no extension, LX has an extension.
Both should be equally safe.

I do not use the car seat.
The problem is not to prevent crashes. Most people do not have problems during a crash. You either survive or not.
Most people have problems in case of an evacuation. The fire after a crash is the most serious problem.
You need to be out of the plane as fast as possible. A car seat does give you minor advantages on crashes, but takes priceless seconds when you have to evacuate. I never would use a car seat because it is more safe without.
Remember a plane is not a car.
I put our car seat - securly wrapped - in the hold.

Airtraffic is one of the most safe means of transportation.