Big difference between the two.

In F eat anytime. J you follow a schedule and generally speaking if you don't eat during the meal tough luck.

You can always ask for seconds....in J mains are easier than plated appetizers. Although usually the loading closely matches pax numbers so unless you picked the thing nobody wanted there's a chance it's out.

F has a better chance but things run out too and frankly my problem in F is too much food not too little. Usually they have seconds or more available of caviar.