From experience with Windows “freeware” some of us have seen what happens when such pop-up notices become commonplace. It is not pretty.
This isnt freeware.
“Free” in free software is free like free speech, not free as in beer.
This is one of the places where english fails. Libre vs gratis
If you don’t like it, don’t use it.
Then you also don’t cause any more cost to the KDE project.
So the reason it makes me uneasy is that at the same time as I do want KDE to succeed, I do not want this tactic of begging for money in annoying little on-screen pop-ups to succeed. If it does, then perhaps it might spread to other free software projects. If all of the hundreds of them that go into a linux distribution start feeling free to make their demands it will be a real mess. As some old philosopher said: To judge the morality of an action, consider what would happen if everyone did it.
I remain an Xfce user. They also accept donations.