for example to quickly unwrap this object to such UV map?
That to me is how I would expect it to look. If the uvmap was all perfect rectangles, then the image on the object would be distorted.
There is “quad unwrap” in the uv window. select one face in the uv window, (make sure all are selected in edit mode, SPACEBAR and search for quad unwrap and apply, it will turn the map into rectangles.
Attachments
QuadUV.blend (1.71 MB)