I haven't used it yet, but there's nothing really that I can use it on, as I've caught all the legendaries. I'll probably just save it in case I find a low-capture rate shiny, since I don't carry pokes with false swipe or sleep moves
I didn't use any of mine. I'm hoarding them in the event of an emergency, such as a Shiny Metang that's about to Struggle itself to death, or a Shiny Drifblim/Solrock/Lunatone/anything else that's hard to catch and carries Explosion. Stuff like that.
I used mine on Landorus. I just really wanted to easily catch a legendary for once. I usually hoard the things to the point that they never get used, and in that case there really isn't a point in keeping them. I guess my other is marked for a random shiny that may pop up.