Rated 1 out of 5 stars

The only thing that this thing does is sending you to a webpage with a search box which shows random links to a bunch of other websites no matter what you type in. It doesn't does what it says and is absolutely useless.

Rated 4 out of 5 stars

This is not a separate add on, it is a search engine addition the same as the one on Mycroft. Although you do have the option to have an extra search box on your toolbar if you want, you don't need it.

This did give me a pretty comprehensive list of hard to find torrents, with the most recent and healthiest at the top. However, it doesn't list the number of Seeders so I probably won't use it much. Clicking on each link to find out if it's healthy is annoying. (I miss Isohunt!)

Rated 2 out of 5 stars

I have not tried this as I just wanted to let people know - you do not need a whole separate addon for this function!
There is a perfectly good working search engine addition that you can add to firefox search engines list, without having to run any addon for it.
Go here:
http://mycroft.mozdev.org/search-engines.html?name=berilium