Ok, so I'll admit I was a tiiiiiiiiny bit worried about the metal plate-or-not issue, so I emailed SSS support and got this:
"You won't have any issues with that so no worries! You have the option to use the metal plate underneath but it is not required"
So looks like the metal plate is added support, average trail riding with a few rocks you bounce off of, no prob, but if you doing something crazy you should probably have the plate in there.