other then the fact its over 80% and that induces vomiting, denatonium/bitrex is nontoxic!
Its often used as the placebo in medical trials!
http://www.sciencedirect.com/science/article/pii/0021968187901871And is also used to stop thumb sucking in children!
There is however an issue with how the ethanol is produced for diggers, it could be using GM yeast or it can be made from cracked hydrocarbons which doesn't involve fermentation, in that case there is possibility of heavy metal impurities and other nasties.
If you cant detect my sarcasm, then this is my final message
Metho is worse then fernet and the bitterness is increasing and will persist on your pallet for a long time with the amount thats in metho
Not to mention it could infact contain nasty impurities, it is however a common misconseption that the impurity is methanol