This tool is very popular, and is not new - surprised you have not heard of it. I would think any list of SEO tools is not complete without this one.
As far as I'm concerned, this tool is a part of Firefox. My web experience is not whole without being able to highlight the nofollow links, the link report and show pagerank as a number instead of a dumb green bar.
Actually, this tool is the main reason I don't use Opera more often - I love Opera, but it doesn't have SearchStatus
My advice is to write your extension that only covers the features this doesn't have, because SearchStatus is already well respected, reliable and polished. It does some simple tasks that you need all the time well, so your tool would need to be pretty impressive to get people to change.
Write something that does not compete with features already working well in SearchStatus, and people will use your tool as well.