I think they are quite different in scope and purpose. I don't know Poser File Organizer, but know PBooost inside out.

From the marketplace info, PFO seems much closer to CorrectReference/CorrectReferencePro also from Hogsoft by Hogwarden. (The former is free, the latter much more powerful than CRFree - or PFO by the looks of it.)

PBooost is focused on switching "banks" of Poser Libraries in and out of Poser's runtime while Poser is running to effectively get around Poser's 255 folders per library limit. This allows for much more organized Poser libraries (even on P4/PPP which do not have sub-folder support). As such it is the program for doing this. PBooost is compatible with Poser 4/PP/5. If you are using it with Windows NT/XP you will need to correct any bad texture references (due to a bug in Poser, not PBooost), which you can do with CRFree or more easily with CRPRo; or perhaps PFO (if it's able to detect every error). For more info on Hogwarden's products check out Hogsoft's website hogsoft.com. PBooost is currently under further development, but existing and new purchasers can buy in confidence as Hogwarden has indicated that updates will free.