With a single steel tank in a 3mm wetsuit and SS plate you won't need much (if any) lead. That's fine if your trim is good in that setup. If you are head heavy (quite likely) you are going to have a tough time ever trimming it out. A lightweight plate (AL, ABS, Kydex etc) gives you the option of adding a small weightbelt which will probably result in better trim. Not to mention many of these lightweight plates are cheaper and with <25dives you likely have other gear needs too.
