The size is only different for the straps the plate is still the same. The ghost is great for travel but it is limited to 15L cylinders, so if you dive large cylinders than 15 then the Ghost may not be for you.With the zen. What size do you have? Less than 175cm (S), or 175 cm or more (L). I am looking for something for holiday diving, possibly a zen or ghost and am under 17T