Regarding the difference between PBB resources and ones produced by LOGOS, I don't have first hand experience, but if I understand it correctly here is what happens. The most basic resource would simply contain the raw text of the author put into Libronix format so the software can load it. This will allow you to read the book with the Logos software and allow for general word searching. For anything else to work someone has to go in and "tag" everything for it to function. So for example, if I have a latin dictionary in Logos I would expect my Logos commentaries etc to allow me to see the definition of the latin word via my latin dictionary. I would assume in the free PBB books that similar tagging has not taken place so I wouldn't be able to seemlessly access the dictionary. Same with scripture references, greek language features and quotes from other authors you may have in your collections. So if you are choosing between "Free" and a logos version it probably comes down to how much value you place on these internal links vs simple "text search". This is how I understand it to work, though I could be way off.

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Kenneth Murphy
M.A.R. Student [Theology & Biblical Languages] - Whitefield Theological Seminary
Covenant of Grace Church - Member
St. Charles, MO