I've never used one but it doesn't look too safe for exactly the reason you state - you can't hit it straight and freeze plugs are tough enough to install.
Dale McIntosh
ACES #1709/TC #92 Gold
67 SS/67 Elky
http://www.dalesplace.com
I haven't seen one of those in quite a few years. It is used to install freeze out plugs that you can't hit straight on. It never worked.
Bob
A.C.E.S. #1164
T. C. #375
65 Malibu
85 El Camino
95 Camaro
