It has a learning curve like any other type of software. It just depends on the knowledge you may already have if the learning curve is higher or lower for you.
I prefer Fusion for generating the toolpaths, not for creating the designs. OpenSCAD doesn’t have that CAM functionality and the Fusion 360 CAM functionality (generating the toolpaths to cut everything) are far superior to what Luban can produce. Both in quality and speed.
The free for personal use is valid for one year and needs to be renewed every year. I’ve renewed mine three times already without any issue.
As already mentioned, you can’t use the fourth axis in the free for personal use Fusion360 license. If you want that, you do need the paid version (and some addons even if I’m correct). Doesn’t mean you can’t do anything, but it needs some workarounds and extra overhead: