It is all too easy to duplicate albums and rather challenging to avoid this + eliminate ones inadvertently downloaded.
Roon is OK at detecting duplicates on identified albums although is not foolproof and, in my case, lists albums that are not repeated. But I hope to have finally hit on best practice to avoid the duplicate situation.
Once downloaded. before editing, check down the bottom to see what suggestions Roon has found in the library for further examination. If you have inadvertently downloaded a duplicate it will show itself there. This check only takes as few seconds and saves time wasted in unnecessary editing.
I have used this check on a number of previously downloads and have come across quite a few duplications, often items only related to the primary album, not a duplicate of it.
And I do not use the Roon delete function. I now have the habit of going back to Windows Explorer to remove the duplicate. Annoyingly (for me) Roon sometimes only allows the earlier item to be deleted. I assume this is because they expect a later version to be better, something which can happen with current reissues of remastered recordings. However I usually prefer to delete later additions as they are usually on a currently used drive.
Hard drive space is inexpensive so duplications are not a serious issue but they bug me so I am taking time to eliminate them.
In the last 8 years Roon has made several improvements although (not serious) irritations still remain. For a time Roon was placing roigue tabs on albums during editing although that has not happened lately. It often tells me I have no tabs before changing its mind and revealing a list in the window. Typing in e.g. an artist name to search does not always go as it should and might have to be repeated. But these are minor issues I can live with and the general search tab at the top is now very good and swiftly locates albums if the title is listed.
Bottom line is Roon fulfils many hobbying lusts with listening to glorious music the very fulfilling reward.