OK I am not a user of DNG myself but I am trying to keep informed.
What specifically are you saying and advising here?
> If you drag the DNG file to the Affinity Application from the Lightroom film strip, it will open in Afinity?
Yes, as was said above, on a Mac you can drag a DNG onto any app in the Dock.
Sadly, on Windows Adobe have never enabled drag and drop to other apps. So on Windows, or if LR is in Full Screen mode (ie the Mac Dock is hidden), just use the plugin. For one app, it's free.
> Will Affinity apply any or all of metadata and edits applied in Lightroom and saved to the DNG file?
That wasn't the OPs question, of course. In any case, I don't use Affinity and can only answer generally. If you have saved metadata back to the DNG, it is possible for third party apps to read any metadata, even adjustment values, and also to display the adjusted preview that is embedded in the DNG. So in a third party app, you can see the results of your Lightroom edits. That's one advantage of DNG.