My major concern is they state that you should not provide supplemental calcium in any form. That is contrary to almost all feed manufactures and publications that I have have delved into, ever!
Chickens are VERY aware of their calcium needs, they don't just eat it to eat it if it's offered as a side, so as long as you don't mix the 'extra' into their food forcing them to eat it they will do a knock out job of self regulation of their calcium intake...