Yes, it is quite easy to add a new column to the GUI. However, it does require extra thought into performance.
The main issue here is that the code written for the Data Extender will execute for every item in the folder. For example, let's say it takes .1 seconds to execute the code per item. For 10 items it adds 1 second to the time required to return the list. For 100 items we would add 10 seconds.
Now, maybe that is still worth it, because it would take more than 10 seconds to lookup the revisor of each item manually through the GUI.
The best approach I have used is to set a metadata field on the folder, structure group, or publication to enable the Data Extender. By default it is off, but if the metadata is there then the GUI Extension code runs.
I recorded a 40 minute step-by-step walkthrough on the Tridion Community webinar where I build a Data Extender. It was with Tridion 2011, so it is possible some small things changed (with dlls), but overall it is the same.