You cannot practice calligraphy with pen copybooks for two reasons:
1. From a historical perspective, there were calligraphy with brush first and calligraphy with pen later. Pen calligraphy originated from calligraphy with brush and calligraphy with brush. It has been around since ancient times, but writing pen calligraphy is still a modern thing. Even though the use of pen calligraphy is quite common nowadays, it cannot completely replace calligraphy with brush. Children are born from their parents, can it be the other way around? Of course not. This is also an important reason why the art of Chinese calligraphy (especially brush) has endured for a long time.
2. From a practical point of view, using pen calligraphy to write brush calligraphy is a waste of time and effort. It may produce some effects, but in the end it cannot achieve the expressiveness of brush calligraphy and can only write Simple and blunt lines and structures. On the contrary, it is possible to use a calligraphy brush to write pen calligraphy, and it can enrich the expressive power of pen calligraphy.
Due to time constraints, I can only say this. I hope it will be helpful to you.