I have hard time seeing differences between ModelLayer (model) and FeatureModelLayer (feature_model) and when is the best to use one or another.
It seems to me that you can achieve the same from both of them when you use model with feature_geom as drivers, like using features (to connect to database), styles, layout, etc.
Am I wrong, or if they provide the same functionalities, which one could be the best choice in this context (features + styles with selector + layout)?
The FeatureModelLayer is a replacement for using ModelLayer+feature_geom. We are moving away from the "driver" concept in osgEarth 3.0. So you should use FeatureModelLayer moving forward when rendering from feature data.