The vasoline smothers the mites. I have one Buff O hen that every now and then has a flair. I treat her legs with vasoline, spray the roosts with Seven liquid, check the whole flock for mites, and so far have only had to do preventative treatment with Ivermax under their wings. My hen responds fast to treatment. Raised scales flatten and look pretty much normal. I think the vasoline also helps moisturize her legs and aids healing. If your leg mite cream works for you by all means I would continue with it only make sure you use it regularly so the infestation is gone for good. No sense creating pesticide resistant creepy crawlies. I'd also give them pro-biotics and vitamins while you are treating. Those mites are sucking blood from your girl. Also when you are treating, I would use Seven powder and dust down your nesting boxes also. In for a penny in for a pound as the old saying goes.