I'm just thinking whether I'll feel a smaller bladder ?
Its not like the bladder size bothers me.
I don't dive/swim fast - so theres no question of drag.
Who even dives so fast that they would feel bladder drag?
Single bladder comes in various sizes from ~10kg upward.
Only you can answer that question.
I can feel the difference myself but that is me.
You came here because you have doubt about the size of the bladder.