Here are the key reasons to use the new updated API provided by GroupDocs.Comparison for .NET since version 19.9:
The Comparer class introduced as a single entry point to compare documents of any supported file format with various options and ability to accept/reject differences in output document.
Document compare options for all document types. Instead of using document related options now options are related to compare type only.
The overall document related classes were unified to common.
Product architecture was redesigned from scratch in order to simplify passing options and classes to manipulate comparison.
Document information and preview generation procedures were simplified.
How To Migrate?
Here is a brief comparison of how to compare document with old and new API.