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Yes, channels with threshold works with some images but for the more intricate clean cutouts I find it lacking.
I looked at your other suggestions:
OnOne Perfect Mask seems to be more global and some of the examples lack accuracy for my needs...
Fluid Mask 3 might be for me - the tutorials are fun and I will download the trial version. (many years ago I used KnockOut from Corel and this seems to have a similar approach)
Thanks again, Bee
Then I'd suggest that you add to your knowledge base on masking: Photoshop Masking & Compositing: Fundamentals.
Luminosity masks, and the Calculations and Apply Image commands used in conjunction with Blend Modes are far more accurate than third-party masking plug-ins. As Deke McClelland says, these functions allow the image to select itself. And third-party plug-ins all have learning curves and their own idiosyncratic behavior; some, for example, can't create masks on a background layer.