Yeah, I know, but if you're dying to catch a wild shiny without hacking that's the easiest way. (unless you only want a 5th gen pokemon.) And it's for any wild pokemon you can catch in grass.
fffffffuuuuuu legendaries What you should do is check the GTS religiously for them. I mean, it's tough because most of the time when you see one they're asking for a really rare pokemon in return but on occasion I've seen pretty easy trades. (which are almost definitely hacked, but still, it's not like you're the one who hacked them.)
Sorry to say but picking any shiny out of those three is a less chance unless you want to keep on turning off then turning on your game again till you get them.