It's a decent tool but it has a bug(s)! It does finds the dupes o'right but it also cannot distinguish between nuances of urls. e.g. I saved bunch of google searches for later, it sees them all as one dupe! And regarding real legit dupes, there're no commands or buttons to deal with the dupes in one fell swoop but rather you have to sit there and manually click on every dupe checkbox to take action.

The Find Broken URLs is a good feature but many websites like linkedin, facebook that do not allow webscrapers see it as a threat causing BookmarksCleanUp to generate a false positive report that the bookmark is broken or dead. The average person using this add-on needs to see friendlier http errors such as "the target web url does not allow remote checking!" as opposed to http 404!