Thankfully, I've never seen one discharge, but I was of the opinion that Halon is strictly a gas. Believe it functions as a "smothering" agent by molecularly gobbling up all available oxygen so that the fire can't use the oxygen and dies out. I've heard that if you have a Halon discharge because of fire, that you should NOT open the hatch until you are sure that the fire is out, or you are sure that the Halon did not do its job.
I've got automatic Halons on the Sea Ray, and one on the Formula. Be aware, though, because I think the Halon extinguishers do not count as your Type ABC handheld that the USCG requires.