I have the Saddlemen Drifter's in the large size but not the EZ brackets. I have them hard-mounted to my saddlebag brackets, they only come off with tools. Can't imagine riding without them so the EZ brackets wouldn't pay for my use.
Bought the bags from Accessories International, great price and quick shipping. With their rigid back, I don't believe you will need any additional bracing. So far, mine have been great. Like someone else pointed out, the large size holds a jacket. I don't like the looks of the Jumbo size unless you are running a solo seat, than they look perfect. (my opinion) The large size fit my cruising needs fine.
