I tried using it in the free version, but was never able to figure out how to export the heightfields.
The Gaea FB group, of all things, is where the action is on that software.
Dax is there all the time answering questions and bug hunting, like Boss Fairclough is here.
Right click in the last node, usually erosion, and choose SAVE
Then click on the build manager in the upper right.
Choose you resolution and file format.
File destination is set in the preferences, which is a a little weird, I hope they change that.
Some of it is a little bizarro, but once you get under the hood you'll be fine.
Off to the races.