I have numerous brass cased Scubapro Balanced Adjustables and I like them as they offer excellent heat exchange and virtually no dry mouth.
Brass cased second stages are also incredibly durable and I own some that were made in the late 60's. Even after 40 years of use, they have only minor scratching and look much better than the average 2-3 year old plastic cased second stage.
If you ever drop a tank on a plastic cased second stage, you are done diving until you can get the case replaced. Do the same thing with a brass cased reg and, at worst, you'll have to knock out a dent before you continue your diving day.
Plastic cased regs were NOT an improvement in diving technology, they were just a means of reducing production costs and increasing profit margins for scuba companies.