I've come across MBA Math - a service that helps develop various business skills for those preparing to apply for business school.

As somebody whose entire career is in the life sciences field - PhD / postdoc mainly - this is very interesting to me.

Does anybody have any experience with it? How useful is it?

It seems okay for such a low cost. I would also consider https://www.edx.org/course/maths-essentials

Or Coursera classes.

Based on your background, you might already have a lot of the skills they teach. It might be better to target weaknesses with specific courses - the beginning specializations in the Illinois iMBA program are free through Coursera.