Best way to find the old posts is to do a search on T-rex Dragon dust. The gist of the discussions in the the past about this product is that it could have harmful effects on dragons, mostly dehydration, impaction and loss of apetite/activity. The discussion started when a frequent poster here mentioned a type of ingredient in the product that was known in the past to be a harmful form of fungus though the form actually in the dragon dust is not the same thing.
I personally haven't had any problems with the product or others in this line of food by T-Rex (ie The Crested Gecko Diet). I don't the dragon dust every day but every other day. I find it tends to dry out greens and which is, in my personal theory one reason why some dragons may be more dehydrated. Other users may have failed to stop using other suppliments with the product as it is not designed to be used at the same time as regular calcium and multi-vitamine supplimentation.