You can load it with a few sea pearl bags at your destination. It puts the weight in the same location. No extra drag like pockets. It even will allow some slight weight trim if needed. Yes an additional $18 but that is a lot less than the difference in price of SS vs AL backplates.
Many / (most?) travel destinations have only block weight available. Are you going to bring the lead shot with you? If soft weights are available are you planning to purchase them, cut them open and pour the lead shot into the sausage? What do you do when you travel home or to the next stop on your trip? Repeat as necessary? That doesn't seem to versatile, cost effective, or even responsible.
Your argument is versatility. What's more versatile than a SS plate that you can use at home and when traveling?
Look at the typical warm water rig, 3mm wetsuit + an al 80. The wet suit is about +4 lbs buoyant, and the empty 80 is about +4. That means you need about 8 lbs of ballast. A SS plate and harness is about -6 and reg is about -2. Bingo! Many divers use nothing but the plate, harness and reg for ballast in warm water.
The advantages of a SS plate in cold water should be pretty obvious.
Why have lightweight plates at all? Big steel doubles in warm fresh water is one good reason.
Travel to places that require cutting your tooth brush in half is another.
Most people don't see either extreme. That leaves SS plates as a better choice for most,
even those that travel a bit.
Tobin