Hi,
Yep, very usable.
It does things differently to OziExplorer, but the two can interchange the same files.
One big advantage is you can download an area off the map or along a planned route. Thus you can have an area of satellite imagery well off the network.
You can sync your tablet with cloud.hemaexplorer.com.au and share trips, tracks, photos etc with selected others or public or keep it private.
Neither Hema nor Ozi do turn by turn navigation, as their maps are just images.
However it is possible (with a bit of planning) to use Google Maps to plan turn by turn tracks and import the Google .kml file to Hema. This is handy for complicated tracks/routes on back roads when normal GPS will favour routing you out to major roads.
The Hema app is good value and easer to get started with than Ozi, but not as versatile, because you can calibrate almost any map to use with Ozi, Hema only uses its own (very good) maps.
Cheers

