I already have the Medela Freestyle pump, but found the handsfree hook-up to be too complicated and cumbersome- so I purchased this product.  It is truly fantastic.  I can walk around, type, soothe my baby if she needs it- even change the laundry if needed.  I find that I'm able to pump for longer because I'm not just sitting and staring at the seconds pass by- which has helped increase my supply- a great added bonus!!
I use the belt hook-up that my Freestyle came with to maximize mobility.
I use this over my nursing bras and only when I'm pumping- I can't really imagine wearing it all day instead of a normal bra.
Added tip- I put my breast shields on, then poke the ends through the holes in the bra, then hook them up to the rest of the breast pump valve thing- I think the directions tell you to jam the breast shield through the bra from the outside, but that seemed dammaging to my breast shields.  This works much better.