Bing Webmaster Toolbox: Oh yeah, remember that other search engine? Yes that’s right Bing has a whole collection of tools of their own, including keyword tools. The data will be taken from Bing itself, which means that you should be able to make relative assumptions about keyword popularity. because lets face it, Bing users aren’t that different than Google’s.
So which tool should you use? The simple answer is ALL of them!! If the data from several tools suggests that a keyword may be a good keyword to target, than you should feel fairly confident that it is. If your results appear to be contradicting one another for a particular keyword, then you may want to be hesitant in including that keyword in your selection. SEO professionals should never rely on one resource for research. No one tool is going to be 100% accurate and you stand the best chance at making the correct strategic decisions by using a variety of sources.
It would be great if you can provide comparative analysis of this tool with Google Keyword Planner. Since you’re using this tool so you can provide best comparison. One differentiation which I understood is that this tool works for yahoo and bing as well whereas Google keyword planner works only for Google but Google being a dominating search engine, gives the highest returns, so only this reason may not be enough to buy it.