Well funny you should say that Jim but it takes all sorts in this world they promoted them for years as per one only needed but perhaps because they are quality and most users are metal people who have different needs. Once again I say cheap as chips I have had mine for umpteen years would not be without them for quids, do a small exercise with them I would pay many times their cost cheerfully for the ease and strength on my X Y axis vice. Now this from me who spent happily thousands for Hasselblad Cameras went to America long ago to get a full Mamiya outfit in New York, travelled to Singapore to Buy Discus fish at a hundred dollars each in the 70,s call me enthusiastic if you like.
Each one of those prismatic shapes can be used with advantage, picture in your mind the bonus of the horizontal grip for pen blanks to allow damage free hands while you finish the faces of you blanks.
I agree to you and me pairs would be the way to go but heck they say one is enough we say two is terrific.
Anyone remember the Triumph Mayflower car? perhaps not but it was ugly as and a good mate of mine bought one and took me 60 miles to confirm my love for my girlfriend, fiance, wife of 58 yrs guess we all have reasons or needs to do everything.
As pen people IMHO we need to cut our cloth and make wise purchases for the long haul. I clearly remember my dad in his eighties stripped his backyard garden of every fruit tree, laid new paths planted around 30 new fruit trees etc, next door my sister shook her head saying he and mum will never get the benefit of all that work, well guess what he did died at 92 yrs of age hardly a weed ever in his garden averaged about 4 hrs sleep a night for umpteen yrs, his motto if you want something do it.
Okay so back to prismatic jaws they easily convert to X Y vices they really work I have been blessed with a good eye for centre and verticals and find it served me well as a sparky lining up switches, power points, switch boards, when I drill blanks I knock over dozens at a time when I was heavily into Corian 1/2 inch square blanks 95 out of a hundred drilled near dead centre. Every repeating task I devote a corner and something to do it with I hate routine my answer.
Everything shared on forums you notice I this I that well there is a reason cause it works for me Mr average with OH&S, litigeous well meaning people everywhere presenting my take on things is my idea of sharing.
Kind regards Peter.