This plugin will put the top ten search results visitors used to reach your pages, on your site pages - it is very spammy, and may be considered black hat, you are advised not to use it.
There is another thread on this somewhere in the forum, with users reporting de-indexing with this installed, it could have been a coincidence, but... You will be adding unnecessary keywords to your page, for one thing, a big no,no, thus affecting your carefully constructed density (which you have done, of course). Depending on theme it can also mess up the look of your site, and make it look spammy. You may get away with using it, it is up to you whether you want to risk it, especially if you have got Adsense on your site.
it is black hat for shure. i wouldnt it recommend you to do it, like tiddles said - especially if you have got adsense on your site.