I might be missing something here, but after selecting the plugin Nik opens and sets up a new layer in Ps and the edit goes as expected. If I select the brush tool the layer is inverted and Nik hands me off to the brush tool. Using the brush tool I can brush in the areas I want. All that is fine, but when I hit apply it merges the layers down so there is no going back. If I do not use the brush tool it saves the layers. The brush tool is not available when working in a smart object.
There also seems to be a bug in that on some occasions Ps opens without displaying the Nik tool bar. I need to test more but I think it is after using the brush tool