This is just my opinion, and why I personally never bothered with the 2 factor coins when purchasing from him.
I heard this already... I have bought some physical coins so I do not believe that the producer could be a cheater, bad things shouldn't happen with me.
Look at nearly every news story, every Reddit post, they feature his coins. He has given the non-technical person something the wrap their head around in terms of bitcoin.
And that is a problem. He populated the idea that bitcoins could be physical! Its a vicious idea. Now people are searching for a physical coins or banknote to buy. Look at this random guy on a wikipedia talk page
https://en.wikipedia.org/wiki/Talk:Bitcoin#Tokens. People are really seeking for a physical money they once saw on a picture. Thats what Casascius does. And thats why I am shaming him.