I did the mbamath.com course, I did it because my quant percent on the GMAT was so low so I wanted to add this in with my application to show I was prepared for the classes. Although I did it after applying and only ended up sending the transcript to Kellogg, oh well
I have a marketing job now, but not too quant heavy and I definitely feel it helped me. The content wasn't too detailed and I don't feel I got a full understanding of some of the concepts, but I feel much more prepared now. I had seen all those terms and formulas before as an undergrad but never had to use them and I felt this was a sufficient refresher to at least explain the basics and tach you when to use each formula with some examples you'll find in your coursework. There were additional appendix sections that explained more of the math, but I skipped these since they said it went beyond the scope of what you will have to know and more just for curiosity. You get a year subscription, so I plan on reviewing the topics again before school starts. I did kind of rush through it a bit just to get it done so I could still submit the transcript to the school in time before they made a decision on my application.
Get the best GMAT Prep Resources with GMAT Club Premium Membership