We have used the quick disconnects for years.
(Makes me sound old, huh? I'm only in my mid-thirties, but we've been in WBCCI 10 years. We full-timed for two of those years...that's a whole other story.)
In my experience the brass disconnects are worth the extra $$$. The plastic ones become brittle and difficult to use, and then finally break. The FL sun will just make it happen that much faster.
May I make a suggestion? Please paint a hideous color on the disconnect you have put on your black water tank flush inlet. So many parasites and diseases can and will be spread by contaminating your fresh water with any item contacting black water. We don't even store our black water equipment in with any other equipment, especially not fresh water equipment.
I am speaking from experience. I drank water contaminated with Cryptosporidium from human waste. Take my advice...don't go there. It took YEARS to fully recover.