Niche market reserch tool?

Previously mentioned by  Karl Steinmann that Overture is dead, so Larry suggested http://freekeywords.wordtracker.com/
But now Google keyword tool came up with search numbers as well.
So I did a search on both of them on a keyword "air purifier".
The results were WAY OFF for both of them!
Word Tracker showed 346 searches.
But Google keyword tool showed 823,000 searches!
And some other tools I used came up with around 12,000 searches!

So which one should I believe?
Does anyone know why the results differ so much?

Damn good question!

Lets  take a peak at the results

Air purifier

Google: 823k monthly searched

WordTracker: 346 in last 130 days

WordPot: 19,213 daily

Wordpot and google are close. WordTracker is confused.

Here's how I feel about this. There is no keyword tool that will tell you exact numbers. I have tested what I know is fact against googles results and they are off, some keywords off by a lot. With that said what you really need to do is simply gauge traffic from all these tools. Obviously air purifier gets a shit load of traffic so I would start spying immediately and see where you can take things.