I have two csv files which each have a field containing the same feature type but with different field names. I need to compare the values of these fields in the two files to find out where there are differences? How do I do this in FME.
Just use the Change Detector. There's nothing more to it. You can check that the geometry is the same, or just check attributes.
See the description from FME help:
Detects changes between two sets of input features.
This transformer is often used with multiple readers, to identify changed features in the two files. It can identify all features that two input files have in common, and those which are in one file and not the other, such as the additions and the deletions.
As usual with FME, they have already implemented something, so doing it yourself with a CRC Calculator, or feature merging is unnecessary.