I definitely prefer mail order and I notice some breeds ship better than others. Learned my lesson buying from Tractor Supply.
I have ordered chicks by mail a few times, the hatchery almost always adds an extra chick or two compensate for the ones that they expect to die in shipping but we’ve never lost any. I’ve only ordered during the winter and they put in a heat pack. I can’t imagine ordering in summer, especially with the way the mail is delayed. They can live a day or so off the yolk sac they absorbed just after hatching, but they are still pretty thirsty when they arrive.
In my experience they send it next day and you are expected to be available to pick them up right away at the post office when they arrive.
I much prefer to incubate my own chicks, but there has been a time or two that a predator has taken out my whole flock, one time it was a neighbor’s dog. Heartbreaking.