sj, I am afraid that you are the one who got things a little confused.
First of all, let’s clarify something: what do you mean by “coming soon landing page”? As your linked page clearly demonstrated, there is “coming soon/maintenance page” and there is “landing page” in SeedProd terminology, there is nothing called a “coming soon landing page”.
I am happy to use the “coming soon/maintenance page” function provided by the plugin for free, and I hope GPLDL continue to keep it in its repository. If you need the “landing page” function, which is a more advanced function, why don’t you get a license and support the plugin author?