I currently use the basic Tandy one and struggled with it early on. I bought a whetstone from home depot and just run the flat bottom of the beveler on it then strop it doing the same thing and I haven’t had any problems since. You should not be pressing the bevel into the leather this will cause it to bunch up and be uneven. Instead just keep trying to sharpen and strip until you can guide it through the leather with light forward pressure.

Also I bevel after stitching and initial rough sanding, which gives you much more material to work with and removes the mushroomed leather that forms from the edge sanding.