Developing a publish plugin. Some API questions

I don't see any obvious drawbacks to either approach, but since I don't know what LR is doing under the covers, I'm lacking any more technical insight.  If it becomes an issue, we can use Processor Monitor to perhaps uncover what LR is actually doing.

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Curious.

Interesting. I'm curious, what was the file type?  If you right-click the file in File Explorer and do Properties, is there a default app shown? E.g.

"if WIN_ENV then LrShell.openFilesInApp ({ file }, "explorer")"

What specifically happens when you use the code I posted? 

That code comes from my Any File plugin, which is used by a large number of people, and I haven't received any reports of it not working on Windows. (It works on my Windows 10.)

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"3) When collection sets are created within our plugin, I want a collection child to be created automatically. I therefore implement publishServiceProvider.endDialogForCollectionSetSettings( publishSettings, info ). Now the problem is that even if the API specifies info.publishedCollectionSet as a reference for the newly created collection set, it's nil. These are the keys I have under the "info" parameter: isDefaultCollection, publishService, parents, name, collectionType, why, collectionSettings, pluginContext. What's happening here?"

I don't have any experience with publish service providers. Lets hope someone else expert in the SDK will reply.  Unfortunately, last year Adobe folded the SDK forum into this main LR forum, shrinking the number of regular participants from a small number down to 1 (me).

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"1) I see there is an LrShell.openFilesInApp API, but it requries the path to our app to be specified. Isn't there any way to simply have a file opened in the default app registered for that file type?"

Use this idiom:

    local function openFileInApp (file)
        if WIN_ENV then
            LrShell.openFilesInApp ({""}, file) 
        else
            LrShell.openFilesInApp ({file}, "open")
            end
        end