When Chrome 49 still uses, the Enhanced Bookmarks flag has removed because there are some issues with something in the previous 43 era!
If you want this extension: https://chrome.google.com/webstore/detail/bookmark-manager/gmlllbghnfkpflemihljekbapjopfjik?hl=en - at least you have an extension icon like non-omnibox so you can rollback to Chrome 48, 47 and 46...
That's why Google doesn't remove this extension...
UPDATE 2019-Apr-13: It seems like they removed the Bookmark Manager extension from the Web Store.
