I have owned my Visor for about 3 weeks and I had no previous PDA experience. I have had my Magellan GPS Companion for five days and I have had no previous civilian GPS experience (Military is different).
While the Magellan module comes with VERY few instructions, I was able to figure it out in short order and logged 2 caches the same day I loaded the software. You CAN get instructions from the Magellan site in .pdf format.
While I have limited experience in such matters, the things I have seen in this and other threads lead me to believe that the PDA/GPS combo can be much more useful/powerful than a standalone GPS. The two major drawbacks I see to it though are the fact that it is not as rugged/shockproof as some of the standalones and the fact that it is not the tiniest bit water resistant, let alone waterproof.