There are two reviews for you to read:
OnCourseNavigator 6 (rebranded version of iGO)
iGuidance 3 That's an older version but the interface is still the same. Version 4 adds text-to-speech so that it now states the name of the road on which you are being directed to turn.
You might also check out the GPSTalk forum at Aximsite for comments from users of both.