It's not really true that all techniques perform fine if you're rendering just one button.

If you're using a masked CALayer, and that layer's in a scroll view or is otherwise animating around the screen, there's a very real chance that you'll drop frames, just from that layer's off-screen rendering pass. Depends on how big the button is.

Certainly, though, if you need parameterizable imagery, you need parameterizable imagery, and so you can't load them from disk. But you can still make your runtime-generated images resizable!