I asked Doug Gordon, author of "GedStar" (fomerly "GedPalm").
Here's his answer:
The "PAF 1.0" PalmOS application that comes with the free PAF 5.x product from the LDS Church is essentially identical to GedPalm 3.1. The main difference (other than being free) is that it can only read databases that are generated from the PAF genealogy program. PAF can not read GedPalm databases and vice versa.
On the other hand, GedStar 4.0 is an upgraded version of GedPalm, and has a number of new features that the PAF application does not, such as support for viewing sources; searching by index number; improved descendant views; searching from any view; and much faster database downloads. Of course, it can be easily used with any genealogy program that can export a GEDCOM 5.5 file (including PAF). Moreover, GedStar will continue to be enhanced and gain new and improved features.
Considering its low price of only about $12, we think that GedStar is still worth purchasing for serious users of genealogy software and handheld PDAs. Where else can you get so much functionality for so little cost?