My fret caul pushes the ends down first, then when thightened a bit more, it pushes down the middle, while still holding the ends down.
I wish I could get as good as results with a hammer, because it is faster.
I am still experimenting with hammering, but my caul method is so precise, I don't think I'll ever make the switch.
When I do hammer, I have the frets a little over-bent by running it through the fret-bender machine, then with a plastic face hammer, I tap the fret almost all the way down. Then I get a brass rod, which I have smoothed the edge, so there's no sharp corner to make a mark on the fret-tops, I place that brass rod on the fret at one end, then hammer on the other end of the brass rod with a steel hammer, while working the rod along the fret, to the other side.
I get really close to the press-caul method doing this.
Dunlop wire will not dent at all from the brass being hammered onto it, but the brass rod gets slightly dented.
I almost always modify the fret barbs too. Usually shave 'em down quite a bit. i like tight fitting frets, but not to where the neck back-bows from the compression any more than slightly.
I also currently like putting the frets in dry, and then running water-thin super-glue in the ends. It's damn tedious tho.