That indicates you can actually have a "no solder" option if you assemble the boards. That should reach more people.
For pressing the header in, you might consider a small piece of wood with 3/8" hole drilled in it. Back the PCB with the wood, line the hole up with the three holes for the header, and use a vise to gently press the header in place. I would use my press, but if you don't have one, a vise works. Another method is using a drill press as a press.