Ingredients - why have 1 pure oil when you can have a squillion ingredients that will just clog your skin and break you out?!
My main issue with bio oil (other than the fact its petro-chem central), is that there are so many ingredients, and none particularly nice. I'd rather use a nice rosehip or organic oil blend.
Results - I used this to try and prevent stretchmarks with my first child - it did not work. And yet, after using a rosehip oil with my second I was left with LESS stretchmarks.
So in short. It doesnt work and its chock full of ick.