Thanks for the heads up. I grabbed them all. I saw there were two versions of DZ3. One was Defense Zone 3 HD and the other was Defense Zone 3 Ultra HD. They both seem to be the same game, but Ultra supports 4K and also seems to be completely ad free, whereas 3 HD has a big button on the main menu to "remove ads."
So I'd say pick up the Ultra version if that's an option.