Anyone use them? My spinning instructor suggested I get one and told me what model he uses and I am looking at them online and I am sort of confused. Do they come with that strap that goes around your chest or you have to buy that seperately? And for women, do you wear it underneath or above the breast?

The strap should be included. If it's not then it's just a watch.

I think most of us are using some sort of Polar. If you go to the Polar website you can download the manual for each model. It will give you a better idea of use.