Let’s just say there was a slim chance that metal shavings would become a flavoring.
Also, there was another, unrelated risk the whole thing could burst into a ball of flames when handling dry berries.
Mostly it was the latter, actually. And although Devon could have simply fixed that, the salmonella outbreak in 2006 put a number of people off blocks for some time. It didn’t help that poffins became hugely popular the summer after.