There is a difference between measuring an existing angle and setting an angle to perform sharpening. The table is useful, but ultimately the standard is actually measuring the angle. The Edgepro can be used for this, but has a limited range without modification and is not as accurate as the Gizmo, because it doesn't measure the actual angle, but rather you read the mark on the vertical shaft. It doesn't take into account the amount of overhang of the blade edge from the platform for instance. It can't go as acute as the Gizmo or freehand sharpening and the measures aren't as precise or as accurate.
If the edge is convex - either purposely or accidentally, you don't have a single measurement, but rather measurements along the convex curve, so it's easy to measure an angle, but it isn't really the edge of the edge you are measuring. So a truly flat edge tends to be a more acute actual angle and will have those characteristics - more delicate but sharper in the sense of being thinner at the edge. Because of this, you probably should compare a true flat edge with an even thinner rounded edge. So a typical 7º freehand edge is really more like a 12º Gizmo or EP edge. Of course results will vary with the ability of the sharpener to maintain angular precision.
If you switch stones freehanding you have to remember the angle with muscle memory and the accuracy of your muscle memory switching stones introduces an error in angular consistency. Less angular consistency means more strokes to compensate for the variances. Muscle memory improves with practice. With a more precise guided stroke, switching stones doesn't introduce this error (even with variances in stone thicknesses, this can be corrected with the Gizmo by actually measuring it). It at least significantly reduces it to a negligible level.
With both the Gizmo and EP, you can actually make small adjustments to improve the precision between stones, although practically this isn't really necessary most of the time, as you can see the alignment of the stone and the bevel within a couple strokes.