There is one new feature in 1.8.4, the grid overlay:
|US Civil Air Patrol Grid in Humboldt County, California|
There is also one feature that has been removed from 1.8.4, iAd support because Apple has discontinued iAds. This means that the stand alone Scenic Map is no longer ad supported. You Need a Map will also gets access to the online maps option as a free feature in 1.8.4.
Unless a serious bug is encountered, 1.8.4 will be the last version that will run on older devices that are not compatible with the latest version of iOS. If you have an original iPad, you will still be able to download version 1.8.4 of the apps even when later versions are released.