As for “supporting the dev” I don’t really get this concept.

It can be both.

• You love the app, you don’t want it discontinued; you pay to continue the developement.
• The developers have a solid business model without any shady practices and have such an awesome free version that you don’t feel the need to pay to upgrade to premium features; then you may pay just to just your gratitude. Niagara Launcher & MixPlorer are similar examples of ad-free FREE versions.