Tested Magnesium glycinate

I see that Krampoff and Nocram are over 10 INR per capsule about 360 mg of Magnesium bisglycinate. Since these are medical grade I'm assuming they're properly tested.

Now I see all these nutraceutical stuff which are easily half the price - like naturaltein, pure nutrition, etc. And they've close to double the dose in one tablet. It comes out to be slightly over 5 INR per tablet with close to double the dose of Krampoff and Nocram.

Do you know of any independent lab reports on these products? How are the nutraceutical equivalents so much cheaper for magnesium glycinate??