I used my purple one for the first time this month and noticed the smell too! Only a bit more toxic like a gas smell or something also mixed in there. The blue also smells like crayon but the black smell fine.
Anyway, it seemed to work ok, only I couldn't get it to spread
Anywhere I placed it is where it stayed, so it kinda looked like lines and I couldn't smudge out all of them. Maybe if it were creamier.
Is there a way I can effectively heat it up? Maybe I should keep them in the bathroom?