PCS may not convert some models from what I've seen. But it probably does a better job of what it will convert. Here is how I use Cob2FS2:
1. Make a shortcut to it, wherever it is. (I put it in C:\Windows\Command so I didn't have to add anything to the Path and can run it from anywhere, but don't need to anymore.)
2. Bring up the shortcut's properties and set the Start In: field to a folder you can easily open. (I use C:\Windows\Desktop)
3. Put said shortcut in C:\Windows\SendTo for easy access.

Just right click a cob file, chose Send To->Cob2FS2. It will appear on your desktop (or wherever) as Test.pof. Before making a new one, rename/move/delete/etc. the old one.
PCS is better though 'cause you can edit stuff in the POF model and do things like choose the "scaling" factor when converting.