Thanks for testing, Wallace.

You won't notice a big difference in the slopes with very small bevel widths & heights, such as with the defaults. You'll see the difference when you begin to increase those values. Flat uses a linear curve in the bumpmap, so you'll see a more flat slope to the bevel, with sharper edges. The Curved slope uses a spherical curve in the bumpmap, which produces a more of a curved result. The Sinus slope, uses a sinusoidal curve in the bumpmap, which produces a somewhat of a flat slope with more curved edges.

It's a good idea to allow the placement of the bevel on a separate layer. I'll add that as an option.

@Marcello - I've been using Ctrl-z with the script for undo during testing. Not sure why you can't. When you perform Ctrl-z, is the original layer you were on not being selected? What kind of image are you using and how are you making a selection, manually?

It's important that the script works properly with Ctrl-z. Otherwise, it's harder to try out different setting to get the result you're after.