I recalled Oliver mentioning those two flavors as being possibly harmful years ago, he avoided them himself. Did a search and it was from a thread after a BBC show. Some quotes.
@Oliver
"I'm personally more concerned about cinnamon and menthol than I am about diacetyl. "
"Menthol itself. It's probably not a good idea long term, despite being one of the pharmacopoeia's safe inhalants. I found it didn't react well with me personally, so have been following the studies.
On cinnamon - it's cinnamaldehyde that's the specific troublesome ingredient. "
More detail in the thread (it's quite long but informative).
E-Cigarettes, Miracle or Menace? BBC Horizon...
Bottom line from
@Robino1
"Life is a risk.
I chose to live my life in a way that makes me happy.
Damn those who want to regulate how I live my life when it does not IMPACT anyone, other than myself, negatively."