I pop. For me, it's more accurate than probing. And sticking a foreign object into my snake doesn't fancy my interest.
If done incorrectly, you can push the probe straight through the genitals....
As for learning how to sex, I would find a local breeder to show you how. Seeing it in person is much better than watching videos on youtube. And by having someone mentor you, you can know exactly how much pressure you need to use.