Played around with a couple of them and in fact once a long long time ago did a review of one of them. Most likely have a couple of them laying around but these days I can see no personal use for one.
It's not all that bad a way to carry the firearm so that it's not noticed but getting to it when needed in a hurry requires a whole lotta thought about what you wear over it and how you are gonna get to the gun once the need arises. For me that means the use of other carry methods.
I most often wear a t-shirt tucked in which for me would make getting to the gun in the belly band rather difficult or if it was tucked under the belly band then the band would likely be quite visible to others. If you tend to wear a rather loose fitting upper garment and don't tuck it in them the belly band might work better for you.
