Justify your statement.

I'm sure that author spent countless hours working and doing bugfixes, all of which was unpaid. While most emulators are free, I'm sure the authors would like compensation for their work.

If this author wants to "force" you into paying him for his work, that is entirely within his rights. Hell, be glad he lets you demo it.

You seem to like that emulator, I'd say go the extra mile and pay for it. You'll be benefitting yourself and the project.