Yes, it can be effective. Using multiple POVs in a so - called 'one POV novel' can add depth and complexity. It allows the reader to see different aspects of the story and gain a more comprehensive understanding. For example, in a mystery novel, the main POV might be the detective, but by adding the POV of a suspect or a witness, new clues and perspectives can be introduced.
One challenge is maintaining consistency. Since it's supposed to be a 'one POV' novel, adding multiple POVs might make the overall tone or voice of the novel seem disjointed. Another challenge is ensuring that each POV adds value. If not done right, some POVs might feel like unnecessary fillers.