The short answer to the question is that it doesn't matter. The results are what is important, and we use the tool profile that we are most comfortable with. There is no one edge, or angle, or shape that is better than the other.
The long answer to the question of straight vs. curved edge, and the other arguement of flat vs, concave bevels, is that there is a difference, and the answer becomes self evident as we gain experience with the tool. The following could represent a typical path of discovery.
The curved edge is the easier profile for the beginner into "Skewology". It is easier to grind. It is easier to control. And it is easier to see what the tool is doing. This often missed visual requirement is important to the beginner because they are using the tool by "eye" rather than "instinct". That ability to "see" that the tool is riding on the bevel will make it easier for a beginner to roll a curve in one direction than the other.
The beginners skew is less "grabby" and easier to control with a 45-60 degree angle between the bevels. This is because there is a higher cutting force with the thicker tool because it has to wedge the shaving farther away from the wood, and it is easier to work against some resistance. The sacrifice is that the thicker angle will leave a rougher cut because the wood is wedged farther apart to the point of breaking with the thicker tool.
We will discover several things as we learn more about the tool and gain some profficiency with it......
The first discovery is that the skew is a shearing tool, and as such, the sharper the edge the better it will cut. The closer we can get to being able to shave with the tool, the better it cuts.
We also learn that the tool cuts easier and better with a 25 or 30 degree angle between the bevels than with the 45-60 degree angle that was between the bevels from the factory. The smaller angle has less cutting force and the cut surface is better than with the thicker angle because the shaving flows more smoothly off the wood. The sacrifice is that it is more difficult to control and is very "grabby" because there is less resistance to our movement of the tool.
If we like using this thinner sharper tool, We also discover that we cannot grind this thin tool on a grinder without burning the edge, or rolling over a dark blue burr. That leads us to using a stone to dress the edge of the tool, and we discover that is difficult to maintain the sharp edge on the curved profile. So we go to a straight edge and flat bevels that we can maintain with a bench stone or sandpaper on a flat surface.
THEN we discover that the flat bevels are easier to use for a planing cut because we are riding the flat bevel on a flat surface, whereas the concave bevel is less stable because it is riding on a 2-point suspension of the cutting edge and the heal of the bevel. We also discover that the cancave bevel makes better beads because that is the natural direction that the concave surface wants to go.
By this time, the edge profile doesn't matter, we can cut with anything. However, the easier maintenance of a sharper edge keeps us on the the side of using flat bevels with a shallow angle between them, and a straight edge.
Having done all of this, we realize that it is the results that count. We use the tool profile that we are most comfortable with.
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