Jon,
I just purchased the navionics for my Lowrance XOG. I just got it today, so I haven't had a chance to play around with it. The reason I went with Navionics was that they have Illinois and Tenn. on the same chip, where as Lowrance has them on separate chips. (Just the way they divide up the regions). I fish primarily in IL, but take a yearly trip to Reelfoot and didn't want to have to buy 2 chips. When you decide to buy, look on Ebay. I got mine for half the price of new! (and mine IS new)
-Shonn