Most breeders sex their hatchlings by popping, this includes Rich, as I have read posts of his that say he pops them. Popping is, I believe, the best and quickest way to check a neonate. When the snake is just in its first couple weeks, it is easy to get a male to expose his organ(s) with very little pressure on them. BUT this should not be done by anyone unless they have been shown how to do it properly by an experience person as you could still easily damage or hurt the baby if done improperly.
But, as the snake gets a bit older, popping becomes less and less "safe" for the snake in the sense that the organ could be damaged since more pressure must be used to conteract the snake using its muscles to keep their organs in, so probing would be best when it gets bigger and especially for a yearling and older.
I have a herp vet that I go to and she is the one who showed me how to properly pop a neonate and, herself, said it was the safe way until they get bigger. In fact, she does not suggest probing one until they are a bit larger as she feels it is much too easy to accidently puncture the organ. But that is her opinion and her method.
Now, even with all that being said, I think it really depends on which method each person finds best and easiest and which they are most comfortable using as long as care is given not to do damage. It is very, very advisable, though, for anyone wanting to sex their own snakes, to be shown how first by someone who knows how, is careful and is successful at it.
Just my opinion on this issue.