There are a number of supplements that assist in lowering BG levels, the ones you mentioned and others like zinc, vitD3, coq10, K2, for example. Should you be taking them depends on whether or not you are deficient. Other factors come into play, like possible interactions with any kind of medication or health condition. How much is enough or too much per individual will vary.
Your doctor should also know what you are taking so they are aware if they prescribe something for you. I take a number of things, but I have multiple health conditions. They certainly make me more insulin sensitive. So that lowers levels for me, keeps me stable and is helping me manage different conditions, but it's taken me years of experimentation.