This probably works fine if you're on a fast Internet connection or otherwise don't need to queue feature. This was the main reason I started using the extension but it required far too much babysitting. I have slow Internet so I set the queue to only run one download at a time. However, it would often start a second download even if one was already running. I would then have to cancel the second download and try again until it just got added to the queue.
Although a smaller issue, the status bar isn't really a toolbar. It is actually an addition to the current page and obstructs access to the bottom (or top) of the page and you can't scroll the page to make the obscured section accessible.
I have switched to Simple Mass Downloader as the queue seems to work well. It isn't exactly "simple", but works fine once you get used to its quirks.