I dust feeders with Repashy Calcim plus every other feeding. I keep a small amount of calcium without D3 in the hatchlings' enclosures but not for the juveniles or adults. There are other ways of doing it but this works for me.
I dust my crickets with a mix of dry crested gecko diet,calcium w/o D3,and a general multivitamin (don't remember the brand). I use it for my Leo,my girlfriend's frogs,and my tortoises (mainly dusted on their salad,though occasionally on dead bugs or raw minced chicken).
Some people say you always need calcium in the enclosure and some people say you should never use calcium in the enclosure. Some people feel that the gecko can self regulate when it needs calcium and other people feel that it's way too easy for a gecko to get too much calcium. What works for me is to let the adults get their calcium from dusting the feeders only. I found that a few of my young hatchlings seemed to be developing early signs of MBD so I put the calcium (without D3) in the enclosure and it cleared up.