Tool for detecting and removing duplicates? [Available in 8.10.18]

In an ideal world, nobody will duplicate data at import time, but actually it will happen. I will not discuss how it can happen or can be avoided, only that it will happen - proof is this thread and others. Duplicate items are not always user error. Switching to a decent password manager often means merging from multiple sources, then consolidating: import from previous password manager plus Chrome's plus Firefox's plus Safari's internal password managers.

One does import once directly after account creation, then never again. You at Agilebits do it never again, so you don't see really any need for postprocessing aid. However, for a new user it's crucial, it's a barrier.

With duplicate items I mean login items that contain the same userid+password combination.

What I propose you can do about this:
- give an overview how many items match above description, in a similar way Watchtower does this. Also create filters, so the user can see a list of only matching entries.
- also give an overview how many items match with url+userid, but different password. These might represent current and obsolete entries of the same login. The category could be something like "unable to merge", "merge conflict" or "password mismatch". Also make a filter for these.
- explain if duplicates are distributed over multiple vaults. If 2 vaults contain the same, because the user imported the same 2 times, the user should see this and the easy fix for the user is to just delete one of these vaults
- make it clear over how many different vaults how many duplicated entries are distributed
- add the opportunity to "merge" duplicate entries in one vault, in spirit similar to functions to merge different address entries in address books in other apps. Merge only items within the same vault.
- this merging would be available from the context menu you get if you select multiple entries. Merging candidates are only taken from the entries the user selected.
- This merging functionality could find login entries with same userid+password combination, then choose the oldest entry as "merged" entry. Then merge all URLs from the other entries to this entry, the same with any custom fields and sections with different values (don't add custom fields with same title+value multiple times). And merge the password history of course. Also skip merging for history entries with identical password+timestamp combinations. After merging, add the tag "merged " to the merged entry (so the user can find all processed entries and can check if all is ok). Then delete the items their content was merged into the merged item.

It's an investment in getting new users. I bet the turnover rate from ex-Lastpass users would be higher if you had such a functionality.
When I was new, I merged entries from Password Safe and Chrome. I almost gave up, because it was so tedious - after all, Chrome autofill wasn't that bad, and Password Safe for just a local vault also wasn't that bad for all non-browser login items. A month after the trial expired I gave it a second shot and decided to do the tedious work.