If all the tool is doing is adding keywords to the keywords meta tag, it's probably useless. None of the major search engines pay attention to the keywords meta tag any more.
If it's adding random keywords to a content area on a page, it will probably degrade the professionalism of the site. I've seen some tools that stuff keywords into the footer on each page. It looks confusing to users, and if the text is hidden, it could get the site penalized.
I agree with Avi that Wordtracker and the YSM keyword tool are the best tools or keyword research. I use them both and you can learn a lot about how people search.
You should determine a keyword theme for almost every page in your site and then work those words into the proper page elements.
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Junior Poster in Training
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since Aug 2005