I use Diigo mainly for simple bookmarking and tagging functions. The 'redesign' of the extension has made it nearly unusable even for that, and the add-on seems broken at times.

1) The sidebar was the most useful thing about it, and that's now gone. The only way to access bookmarks is to actually go to the website, making the add-on largely pointless (for my purposes) other than as a shortcut to create or edit bookmarks.

2) Just now, I had to bookmark and tag the same page FOUR TIMES, because every time I clicked 'save' it brought up a pop-up ad about upgrading to a paid Diigo feature (a feature unrelated to what I was currently doing, fyi). When I dismissed the pop-up, it obviously canceled the bookmark save function along with it each time. (This was using the keyboard shortcut to save a bookmark. I ultimately had to do it by selecting the function from the toolbar icon menu instead, which did not prompt the pop-up upon saving.)

3) When a page is bookmarked, a little bar shows in the top right corner with (theoretically) tools for annotation and whatnot. Only most of the time that bar is completely blank (broken). There is no way to dismiss it, but it often ends up blocking important parts of a webpage (such as a logout link).