Using a press is easy enough. You just have to be careful and firm, while making sure you are lined up.
I have a press, but I hammer them in more often. Either way is fine. I can't say one is better than the other. You always hear people talk about deformed frets, but I can't imagine how careless or drunk a person would have to be to deform quality frets with a proper plastic tipped mallet.
Scott, if you don't have the exact right caul... say you are doing a compound board and it goes from 10" at the nut to 16" at the bridge... you would use the 10" to seat each fret at the ends first, then use a 16" to seat the middle. In effect, this works the same as having the fret over-radiused and pushes the tangs slightly sideways so they are less likely to pop up.
But like I say, hammer is just as good if you have a firm hand.