I have a set of f2 and a set of cateks. the f2 bindings flex alot i mean enough to make me wonder sometimes. the step up to cateks was hard because they have absolutely no give, none. the change makes you rethink your entire technique and it made me realize that the boots I had were to soft. you might end up buying stiffer boots if you go to cateks. I would also suggest the snow pro race binding. it has similiar construction to the f2 but is beefed up considerably. your son isn't big enough to worry about breaking them yet.
D