I've done both ways. 6 years ago, the spring after I retired, I hand planted 3500 oak, pine, and spruce. Just worked steady at it, and about 6 days had them done. Good survival. The fall before I dragged a sub soiler tooth bar where I wanted to plant, and that slit (although closed) cut the sod and helped plant in the spring. The rows then helped keep the trees lined up for later spraying for competition and for mowing around them. Other than that, I'd rather not have the trees in rows.
If using the planter, be sure to have someone that can bend over at the waist while seated. I tried that and it didn't work for me. I'm not fat, but still enough spare tire to make bending difficult, if I also wanted to breath too.
The suggestion to have someone walking behind to 'step' the trees in is a good one if in sod. The packing wheels sometimes don't quite get a good pack around the roots.
Very quickly, the exposed roots can 'air dry' enough to kill the tree. Biggest reason for non-survival, IMO. There is a 'dip' that will help keep the roots from air drying, that you might ask about.
Also, the guy walking behind and 'heeling in' can give the planter instructions to 'plant' the next tree to keep the spacing what you want. Otherwise, its hard to ride the planter and not get them too far apart or too close together.
Having enough tractor to pull the planter is a consideration as well.