Li Xiaofeng

The first one is just attempting to provide an analysis by comparing the two files in the same way you would expect an analysis when comparing a document with your translation memory.  So it effectively gives you the ability to calculate the analysis after the work was done when you know for sure what changes were made... so a post-edit analysis.

The second one is simply showing you what changes were made.  Could be useful if you are questioning payment for post-editing work, or for sharing with a translator to show them how they could have saved time when post-editing by making different types of edits... things like that.

Li Xiaofeng said:

By the way, does this plugin have any other feature apart from comparsion of before- and after-translations?

Yes.  You can also use the ability to create snapshots of a project to actually revert the project to a particular version.

Li Xiaofeng said:

And does this one will overlap with Qualitivity in post-editing? 

A bit.  But my own take on this is that Qualitivity is more of an academic tool as it does a lot more in terms of being able to support keyboard tracking and movement up and down a document you are translating.  It also supports pricing and TQA, so it is a different sort of tool.

Post-Edit Compare is a brilliant tool for production activities.