I used one many years ago and as crude as they appear they are fairly accurate though I wouldn't use one for very light pistol usage. For rifle they were very good. I still have mine & the glass is still intact and & have the regular and magnum charge cylinders.
Buffalo Arm Co. 'was' selling these several years ago but I just checked and they are no longer listed.
Technology and accuracy plus cost of manufacturing probably didn't help their cause either.