"Besides the the added weight and increase in pressure, what are the up and down sides of each?"
An AL 80 and a LP Steel 80 weigh about the same filled, the real difference as you breath them down the AL80 gets positive and a steel tank gets negative so by 500psi when you are doing your safety stop the steel tank will require 6 pounds less lead to stay neutral. That’s 6 pounds less you carried onto the boat :)
For beach dives I use a Steel 72, it has more than enough air for a shallow dive and less lead to carry over the sand.
IF I’m diving with a 3mil suit, my 6 pound BP and a steel tank I have no ditchable weight so for that I need to switch to my plastic BP and then I have 5 pounds if I need to ditch.