I have found the shavings to be useful, but a lot of work comparatively. I would rather spend that energy preparing a finer tinder. Firecraft is all about prep work. There are no short-cuts, even though "it" always seems to suggest otherwise.
Although, the magnesium shavings can be kept from blowing away if you remember to build a decent windshield. The reflector that is part of every campfire that functions at maximum efficiency should suffice.
I personally believe that magnesium shavings are an insult to expert firecrafting, but their usefulness in a dire situation will always be debated, remembering that "insult is always preferable to injury."