As you can see, the BB compact is larger, pointier, and bulkier than the MAC compact. Also, the numbering of the BB powder is funky. I use the third darkest shade Soft Sand, or number 5. This throws me off because in the foundation range my number is 3.5, Warm Beige. The MAC powder uses the same numbering as the foundation and in both I am an NC25.
Both compacts have a mirror and come with a powder puff.
Both powders are very sheer and don't deposit a lot of color, which is what I wanted. Both powders are very silky, blend in to the skin, are great for setting my face makeup, and control my minimal shine. I really couldn't tell much difference between the two when worn on my face. Considering that I like the MAC packaging and numbering system better, I am now going to stick to the MAC Select Sheer powder. Oh, and the MAC powder costs $23 for 12g of product and the Bobbi Brown powder costs $34 for 11g of product, so clearly MAC wins this battle.