no need to worry about the blades, even the heavier X-acto for wider blades stays in. There's no danger it will tople over. Not even with a rounded tip blade.
In fact, the main reason I mounted the foamboard in a photo frame, is because without the extra weight you easily lift the tray up when you pull out a blade.
Even with all the other stuff on it.
What I won't dart in, is my pin vice, the weight will likely cause a fine drill bit to break.
Can also just tape a piece of foamboard to a desk, but can't move that of course.