Airbus test pilots do recommend feet up on the pedals for take off and landing. Feet down are acceptable tho but not their first choice. They speak about it in one of the WIN videos by Airbus. The CBT also illustrates feet up on the pedals. I used to put my heels on the floor for take off and up for landing as FO but now it’s always feet up and I’m loving it. I like having the same feet position for both take off and landing. I feel much more in control also.