Hi, I haven’t had any issues with the hardware for Gucci, but I do wipe the hardware part as soon as I’ve finished spraying. I’m probably too careful, but I usually direct one spray first in the atmosphere to make sure that the protectant is atomized well (eg, no big droplets, should be fine mist), and then I spray on to the leather from a distance of about 3-4 inches away. One coat, then let it dry for 2-3 minutes, then I do a second coat if I think it needs it.
Haven’t tried it on my new Chanel bag - so can’t give feedback on that unfortunately. I’ve used it on my blue Valentino rockstud spike bag, which has a lot of hardware and is similar in texture to chanel lambskin, and I haven’t had any issues so far.