String attribute values should be represented in a monospaced font rather than a variable width (serif or sans serif) font. Otherwise, it's too easy to miss subtle details like duplicated characters that happen to be narrow and look like one in variable width fonts. This is a standard in software development environments; FME should be no different.
"Setting text in a monospace font makes it easier to identify characters by themselves. Because of this, tasks that rely on the easy identification of specific characters, such as programming, benefit from the use of a monospace font." - https://www.techwalla.com/articles/proportional-vs-monospace-fonts