I have been practising on realistic faces too. Now they are with no visible lines. The faces are just shades.
But my actual art targets are different. The next three months perspective and shading. And three to six months hands and folds.
The focus on realistic faces is less mainly because I have only a mobile phone with me. And practising realistic faces is not possible with it. You need a large set-up for getting into realistic portraits. Printers, scanners etc. But I did draw two arbitrary faces. They are just shades and there are no lines.