Yes Hasselblad do make a hand grip (3045154) which is what I think you are referring to. Yes it works well, although it's neoprene and not leather. Easily adjustable, secure and comfortable to use. I find it gets in the way occasionally when I'm using the camera for landscapes on a tripod. It makes reaching some of the smaller buttons on the camera front a bit fiddly. I keep hitting the strap when I'm reaching around the grip to access the buttons because my hand isn't on the grip and through the strap as it is when handholding.
I'd miss the grip if I didn't have one.
Hope this helps.