I've used the BTZS dark cloth for years and like it o.k. but I was open to something better so I tried a friend's Black Jacket. The Black Jacket kept the ground glass a little darker inside because it doesn't have the opening slit that BTZS has. The downside was that to avoid the slit Black Jacket has two sleeves through which your arms are inserted much like a changing tent. Each time you get in and out from under the Black Jacket you have to get these sleeves on and off your arms, which I thought was a major PITA. So it was very easy for me to see why I ever did without it and will continue to do without it.