Actually I surveyed a number of Xmas tree farmers and they recommended using the hand-held power auger approach. Mixes up the soil and provides for better backfill / no air pockets. They also said to avoid using a
3PH PHD because you cannot get the tractor aligned right for every tree or its difficult to use on side hills.
Last year I ran a subsoiler down the rows and then we used a dibble bar to plant them all by hand. Wasn't too bad - my 15 yr old (in the picture) did all the digging. The concern raised by my xmas tree advisors was that a shovel or dibble bar makes a single cut that can root bound the seedlings or leave air pockets, whereas the auger approach allows for the roots to spread out.....although last year I had less than 10% failures.
I'll update on how this works......I may just end up running the auger without the harness approach. If all else fails its back to the dibble bar / planting by hand.
PS - Jon Bud......thats my 15yr old in the picture not me. I'm 50 now and paying for years of racing motorcycles; baseball; skydiving; etc....with a bad back & knees....hence the auger hanging harness idea.