The resize/crop handles in GIMP are really big and easy to click:
Could you use the same type in XnView ? It's annoying to have to aim the mouse onto a tiny black box when you're used to just clicking anywhere along the left edge. It's not like the space is being used for anything else.
And also please make outer area (beyond the crop rectangle) darker it's suitable to preview the result of cropping while adjusting crop area
But I don't think what big crop handles will be good... I think it's good enough now, as is. Big handles will disfigure picture.