Found my pix of the tool.
The important features are the slender blade (less root disturbance of the parent plant), the sharp tip, and a stiff handle to withstand prying, when removing the pup. 3/4" steel water pipe is not stiff enough, but 1" will do.
I bought and made a number of tools before I broke down and spent the bucks to get this tool, and haven't needed to replace it in 3 years.