I just copied and pasted the final script - works for me. Also here's the actual .scad file
finned-rocket.scad

As far as hard to learn. It really helps if you have good 3d visualisation. I can pretty much look at anything and break it down into shapes. Plus while I have absolutely no artistic ability when it comes to drawing stuff, I can visualise pretty much anything in my head and then use opesncad to make it.

For me it's immensely easier to use than a mouse based cad package.

We are all different :-)

And once you learn to simply type the brackets automatically and write a few basic scripts - you'll be surprised how quickly you start to model pretty complicated things.