Could maybe wearing a sock help to protect against these risks? IE wear a thick sock and spray the socks (instead of feet) with the flex seal and you have less cancer/allergies?
Maybe if they took the brand out of it, it would be a good idea. I went through a Vibram phase a decade or so ago. I really enjoyed it; being unable to wear them at work, and the added difficulty of putting them on and off eventually turned me off to them, but I felt the concept was great.
For me the worst part was wearing them on any hard flat surfaces always made my feet hurt, I have a high arch and it felt like the pain was due to not having enough support