Improvements/Fixes
The UI had some quirks about it - like the button press wasn't very obvious, and controls didn't really look disabled when disabled, so expect those and some other UI polishes to come your way.
Response to user feedback
In addition to that, I added a little preview area under the Expression text box, which displays the layers themselves as an expression. That should make the layers a little easier to follow and understand.
License callout
I've renamed the license type to STEAM COMMERCIAL down in the info area to make it clear that Height Lab can be used commercially. The EULA says that you can, but not everyone reads those.
Try before release
You can preview this update for both the paid version and the demo. Just right click Height Lab in your library, click Properties->Betas->Beta Participation->beta - public beta.
Enjoy!