The lens module seems to be helpful when I don't use a flattener, however in its current state it is needlessly hard to use. For example, from the shape of the stars I can see where the symmetry center is just by eyeballing, however I have to translate that into pixels to use the Center X/Y sliders and I have not visual feedback.
Wouldn't it be very simple to implement a click as a translation to the center X/Y sliders? Alternatively or additionally (and perhaps people would like that more), there could be a crosshair showing up like in the crop module.
Apart from this simple that would go a long way, have you ever thought about scanning for the shape of the stars to propose a symmetry center and curvature setting automatically?