Anyone know why it is 이것을 and not 이걸?
을/를 is the object particle. 을 was added to 이것 to make it the object that is being acted upon. I think 이걸 is an informal way of saying 이것을.
They are both fine, I think. 거 and 것 are the same, and they become 걸 and 것을 when adding 을.