As long as the boot fits your foot I don't doubt the strap system. I had F20's (previous gen F boots) and never had the laces slip. The lace locking system is solid. I would worry a little bit about trying on salomons in the store then ordering a fusion type boot online. Since the F boots don't have a separate liner they fit differently. There is less fudge room with sizing with these then traditional boots with removable liners.
Thanks for the advice. I just checked on backcountry and they say it has a removable liner.?