Given you run HB and Autopilot and fish along the TN River there's lots of advantages for you to run LM. Additionally, LM has some very nice maps of Chickamauga and other TN River Impoundments.
There are some areas in TN and even the TN River that have been very recently updated by both Navionics Survey Specialists and through SonarChart contributions, even more recently than LM and are available now for Navionics users to download, as well as other features that may get you thinking about running both map options since HB and Navionics work well together as well.
Navionics has over 18000 HD (1 ft contour) mapping and has a card, Navionics + that allows for region less downloading anywhere in the US and Canada. Generally the Navionics + card runs $199, however they also have the Navionics Updates card that is essentially the exact same thing as the Navionics + card except that it requires an older Navionics card or a competitors card to unlock. Best part, it only costs $99.
We don't just use one crank bait to fish a ledge as there are other colors and brands that work well in different situations. I see mapping as the same. Just another option for you to give you more weapons behind the wheel.
http://www.navionics.com/en/navionics-updates