Lele is right - this stuff (neocalglucon is an example) is an excellent emergency source of calcium, but it is not a supplement.
This stuff is for if your chameleon is sick, or depleted its calcium supply for some reason. Basically, if there is somethign WRONG with your chameleon.
A healthy chameleon doesn't need this under normal circumstances. For that matter, a healthy female chameleon doens't need this if she's gravid, or even after she's laid eggs.
This stuff has become popular as a weekly source of calcium for chameleons, and I have wondered why. I recently found out that several mass breeders are reccomending it to their customers. These breeders goal is to get as many babies out of each female as often (and as soon) as possible.
By feeding mass quantities of food, they have females producing eggs as early as 4 months. The factors that lead to their reproductive system turning on so early also cause it to get out of control. The result is females producing eggs not every 6 months, but every 2-3 months. When they're laying clutches of 50-70 eggs, every 60-90 days, normal biological sources of calcium and D3 cannot keep up. Superconcentrated calcium, in an easy to absorb form, is the only way to maintain this sort of reproductive rate.
These breeders, not thinking what they're doing is unnatural or even "bad", informt heir customers of their practice. And it is believed by many to be a normal, perfectly ok way of supplying calcium.
These drops can cause diarrhea, impacting the absobtion of other nutrients (and water)into the body, which makes them potentially dangerous in long term usage.