You can use Courier Prime or other third-party fonts, but we don't recommend it. Setting a script in a different font almost always causes a change in the page count, especially when the script is sent to a computer that doesn't have that font installed. This is true even if the font is in the Courier family.
We have also found that scripts written in Courier Prime may not display the tops of some letters at the tops of some pages. This is a display issue only and does not affect PDF or paper output.
The company that publishes this font asserts that any pagination or display problems that might arise from its use are caused by Final Draft. However, our research indicates the exact opposite, that this font -- having been engineered without any input from us -- can be problematic.
Using Courier Final Draft is the way to ensure that a script retains its original page count even if it's opened on a variety of machines.