Blend modes: using copy layers or "blend if" with adjustments and filters

I note that training videos by Jim Welninski and Matt K for ON1 use blend modes on new layers of a photo such as you do in Photoshop. After leaving PS and adopting LR I became used to non destructive editing with brushes, so when I adopted On1 2017 I liked the idea of combining blend modes and adjustment brushes or filters. However, I am not confident that I am making the most out of what I call the "brush method". I liked the layer approach for adding some contrast and depth to colour with blends like Soft light or Overlay, but I don't want to return to large file outcomes.

Recently I saw a brief video on You Tube by Blake Rudis showing how the "blend-if" function in PS is applied in On1 PR 2019. This re-kindled my interest in the use of the brush method and a better idea of how to use it. However, after several attempts at editing some landscapes I was left wondering. Am I expecting too much?

I like the concept of applying edits to tones or colours much as luminosity masks do, but some of my edits created a curious colour cast (eg, when applying a darken blend to a high light). Green leaves took on a coppery tint. Had I just pushed the tone too much?

I shall appreciate advice on the use of blend modes in adjustments and filters and any comments at all about your experience