I just noticed some bad behaviour on the stock gizmo's part which I believe has been unnoticed so far: When you hit normal or radial, it rotates so it's in the same frame of reference as the post-maneuver orbit. However, your input is still in the pre-maneuver frame of reference! It's quite noticeable, for example, if you plan a 90-degree turn right, and then start adding prograde. Given the gizmo position, you'd expect to go further along the 90 degree trajectory, but instead the angle decreases and it goes further along it's original trajectory. Very wrong behaviour, IMO, and very easily fixable just by having the gizmo fixed in the original orbit's frame of reference. That's not actually what happens, my memory is screwing me. There is something strange related to that when you try to negate all your velocity, however (like planning a landing), and the prog/retro switch around. That's probably what I was thinking of when I... brainfarted.