See the discussion at Reaper forum:
Here is the line6 page for it:
Pod Farm is the next incarnation of the Line6 GearBox plugin. If you owned that just doing update via the Line6 Monkey is only you need to do. The UI looks much better and you do get dual amp configuration which is nice. Time and playing will show whether there is more tone. It does seem to come with more pre-sets which include the GearBox plugin presets.