I purchased this so I could pump without having to sit, holding my pump.  This works like a dream.  The four pockets are extra helpful because they form a really tight seal around the pump.  I ended up getting an extra 1/2 ounce from each breast by using this device.  The only "difficult" thing about it is zipping it around and that's only because you want it so tight that you'll get a good seal.  I could probably loosen it a bit more and it would be easier to zip.