I'm not assuming. My point is that the dev has to share the revenues with the instances. Without instances, the app is useless. It's not the case so users should give the same.

The other point is that a paid third party client adds a layer what makes the instances less visible. This lack of visibility can lower the donation. Also, you will end with one or two people thinking they pay for the app and so for the instances.

A reminder is always good.