I have the Navionics app on my iPhone and use it regularly. It's great for on the water navigation and marking points on the lake and off the water it's great for examining the whole body of water for those coves and holes you may have never noticed. I've used it several times navigating through dense fog where I could only see maybe 10-15 feet in front of the boat and I feel it is worth the price just for this. It has great depth contours and is pretty accurate...as long as the lake is at the same level as it was when it was charted. That's the only downfall. Last I heard they were working on a depth compensation feature which would put this app over the top. It's already great and I use it almost every time I hit the water but depth comp would put it over the top. I've not used the HD version but I can definitely recommend the standard version.