We have planted literally millions of cabbage, collard, and sweet potatoe plants with units similar to the one in the picture. That planter, by the way, isn't designed to plant "potted" or speedling type plants. It is designed to plant bare-root plants. The planter pictured in the other thread is designed to punch holes in plastic mulch and drop in plants with growing medium on the roots. Some GA farmers use that type planter for watermelons. I don't know about now, but the two largest producers of mechanical transplanters used to be Holland and Mechanical (yes, that is a brand name) They are both in Holland, Michigan.
Practically speaking, I would say you would need to be planting over 10,000 plants to justify a mechanical planter. Under that figure, you can hire a little labor for a couple of days and get the job done just as well.
I realize that if practicality were an issue, many of us wouldn't have half the tractors or equipment that we do.